This material was developed and trialled by staff of the University of Birmingham Careers Centre and subsequently used widely throughout the HE Sector. The contributions of Tom Frank, Eric Williams and Clare Wright are particularly acknowledged. mathcentre.ac.uk © 2004 mathcentre IMPROVE YOUR NUMERACY Many students worry about anything to do with numbers, having done little since their GCSEs. This booklet has been designed to offer practice and explanation in basic processes, particularly to anyone facing employers’ selection tests. It uses material developed by Clare Wright, Tom Frank, and Eric Williams of Birmingham University Careers Centre, where it has been successfully used for some time. Regaining numerical confidence can take a little while but, if you once had the basic skills, practice should bring them back. If, however, you encounter real problems perhaps you should question your motives. Employers don’t test you just to make life difficult. They do it because their jobs demand a particular level of proficiency. If you’re struggling to meet that level, or not enjoying it, is their job right for you? 1. Decimals ………………………………………………………………………………………………. page 2 2. Fractions ……………………………………………………………………………………………… 5 3. Approximations …………………………………………………………………………………… 10 4. Averages ………………………………………………………………………………………………. 12 5. Percentages …………………………………………………………………………………………. 14 6. Ratios ……………………………………………………………………………………………………. 17 7. Answers ………………………………………………………………………………………………… 19 SECTION 1 - DECIMALS The most common use of decimals is probably in the cost of items. If you’ve worked in a shop or pub, you’re probably already familiar with working with decimals. Addition and Subtraction The key point with addition and subtraction is to line up the decimal points! Example 1 2.67 + 11.2 = 2.67 +11.20 in this case, it helps to write 11.2 as 11.20 13.87 Example 2 14.73 – 12.157 = 14.730 again adding this 0 helps - 12.157 2.573 Example 3 127.5 + 0.127 = 127.500 + 0.127 127.627 Multiplication When multiplying decimals, do the sum as if the decimal points were not there, and then calculate how many numbers were to the right of the decimal point in both the original numbers - next, place the decimal point in your answer so that there are this number of digits to the right of your decimal point. Example 4 2.1 x 1.2. Calculate 21 x 12 = 252. There is one number to the right of the decimal in each of the original numbers, making a total of two. We therefore place our decimal so that there are two digits to the right of the decimal point in our answer. Hence 2.1 x 1.2 =2.52. Always look at your answer to see if it is sensible. 2 x 1 = 2, so our answer should be close to 2 rather than 20 or 0.2 which could be the answers obtained by putting the decimal in the wrong place. Example 5 1.4 x 6 Calculate 14 x 6 = 84. There is one digit to the right of the decimal in our original numbers so our answer is 8.4 Check 1 x 6 = 6 so our answer should be closer to 6 than 60 or 0.6 Division When dividing decimals, the first step is to write your numbers as a fraction. Note that the symbol / is used to denote division in these notes. Hence 2.14 / 1.2 = 2.14 1.2 Next, move the decimal point to the right until both numbers are no longer decimals. Do this the same number of places on the top and bottom, putting in zeros as required. Hence 2.14 becomes 214 1.2 120 This can then be calculated as a normal division. Always check your answer from the original to make sure that things haven’t gone wrong along the way. You would expect 2.14/1.2 to be somewhere between 1 and 2. In fact, the answer is 1.78. If this method seems strange, try using a calculator to calculate 2.14/1.2, 21.4/12, 214/120 and 2140 / 1200. The answer should always be the same. Example 6 4.36 / 0.14 = 4.36 = 436 = 31.14 0.14 14 Example 7 27.93 / 1.2 = 27.93 = 2793 = 23.28 1.2 120 Rounding Up Some decimal numbers go on for ever! To simplify their use, we decide on a cut off point and “round” them up or down. If we want to round 2.734216 to two decimal places, we look at the number in the third place after the decimal, in this case, 4. If the number is 0, 1, 2, 3 or 4, we leave the last figure before the cut off as it is. If the number is 5, 6, 7, 8 or 9 we “round up” the last figure before the cut off by one. 2.734216 therefore becomes 2.73 when rounded to 2 decimal places. If we are rounding to 2 decimal places, we leave 2 numbers to the right of the decimal. If we are rounding to 2 significant figures, we leave two numbers, whether they are decimals or not. Example 8 243.7684 = 243.77 (2 decimal places) = 240 (2 significant figures) 1973.285 = 1973.29 (2 decimal places) = 2000 (2 significant figures) 2.4689 = 2.47 (2 decimal places) = 2.5 (2 significant figures) 0.99879 = 1.00 (2 decimal places) = 1.0 (2 significant figures) SECTION 2 - FRACTIONS Cancelling Down When we use a fraction, we usually give it in its simplest form. To do this we look at the top (the numerator) and the bottom (denominator) and see if there is a number by which both can be divided an exact number of times. Hence 2 = 1 x 2 = 1 since the twos “cancel out” 8 4 x 2 4 E.G. 6 = 3 x 2 = 3 8 4 x 2 4 15 = 3 x 5 = 3 35 7 x 5 7 16 = 8 x 2 = 2 OR 16 = 4 x 4 = 4 = 2 x 2 = 2 24 8 x 3 3 24 6 x 4 6 3 x 2 3 Use as many steps as you need to reach the answer. Adding Fractions When the denominators (the bottom lines) are all the same, you simply add the top line (numerators) Eg: 2 + 3 = 2 + 3 = 5 5 + 3 = 5 + 3 = 8 6 6 6 6 9 9 9 9 Remember to cancel down if necessary. When the denominators are different, we need to change the fractions so that the denominators are the same then we can add the top line as above. Suppose we wish to calculate 1 + 1 2 4 From the cancelling down process, we know that 1 = 1 x 2 = 2 2 2 x 2 4 The denominators of both fractions are now the same so we can calculate 1 + 1 = 2 + 1 = 2 + 1 = 3 2 4 4 4 4 4 Sometimes the denominators are not multiples of each other Eg: 1 + 2 4 3 In this case we can make 12 the common denominator using 1 = 1 x 3 = 3 2 = 2 x 4 = 8 4 4 x 3 12 3 3 x 4 12 We can then add these two fractions directly: 1 + 2 = 3 + 8 = 3 + 8 = 11 4 3 12 12 12 12 Eg: 2 + 1 = ? 5 6 2 = 2 x 6 = 12 1 = 1 x 5 = 5 5 5 x 6 30 6 6 x 5 30 2 + 1 = 12 + 5 = 12 + 5 = 17 5 6 30 30 30 30 Subtracting Fractions This works in the same way as addition. If the denominators are the same, simply subtract along the top line: 5 - 3 = 5 – 3 = 2 = 1 x 2 = 1 6 6 6 6 3 x 2 3 12 - 1 = 12 - 3 x 1 = 12 - 3 = 12 – 3 = 9 15 5 15 3 x 5 15 15 15 15 Cancelling down gives 9 = 3 x 3 = 3 15 3 x 5 5 NB: an alternative method would have been to cancel down 12/15 to 4/5 initially leaving an easier sum of 4/5 – 1/5 = 3/5 Multiplication of Fractions It may help to understand multiplication if you interpret the ‘x’ sign as ‘of’. Hence: 1 x 2 means 1 of 2 = 1 2 5 2 5 5 The calculation involves multiplying both numerators and both denominators then cancelling down: Eg: 1 x 2 = 1 x 2 = 21 = 1 2 5 2 x 5 105 5 4 x 2 = 4 x 2 = 8 5 3 5 x 3 15 7 x 3 = 7 x 3 = 21 11 8 11 x 8 88 Note that when multiplying, you can cancel down during the sum as well as at the final stage – it often makes the calculation easier: Eg: 31 x 2 = 2 13 31 13 41 x 3 = 1 x 31 = 1 x 1 = 1 9 82 93 2 3 2 6 5 x 61 = 5 x 1 = 5 244 7 4 x 7 28 Dividing Fractions The trick with division of fractions is to turn the second fraction upside down and then to multiply: Eg. 2 1 = 2 x 5 = 10 3 5 3 1 3 Note that this answer can also be written as 31/3 2 4 = 21 x 5 = 5 7 5 7 42 14 2 7 = 2 x 8 = 16 3 8 3 7 21 Improper Fractions An improper fraction is one where the numerator is larger than the denominator, eg. 10/3 To convert this to a mixed number (one combining a whole number and a fraction), think of 10/3 in the following way: 3 x 1/3 = 1 so out of the ten 1/3’s, nine can be grouped into three whole units, leaving only 1/3 left over. Hence, 10/3 = 31/3 Similarly, 12/5 = 22/5 16/11 = 15/11 21/15 = 16/15 = 1 2/5 (by cancelling) We can also go from mixed numbers to improper fractions: 21/8 = (2 x 8) + 1 = 16 + 1 = 17 8 8 8 8 8 31/4 = (3 x 4) + 1 = 12 + 1 = 13 4 4 4 4 4 Addition of mixed numbers Eg. 2½ + 31/5 = 2 + 3 + ½ + 1/5 = 5 + 5/10 + 2/10 = 5 + 7/10 = 57/10 17/8 + 52/3 = 1 + 5 + 7/8 + 2/3 = 6 + 21/24 + 16/24 = 6 + 37/24 = 6 + 113/24 = 713/24 Multiplication and Division of mixed numbers Here, it is usually easiest to convert to improper fractions and multiply or divide as normal: Eg: 25/6 x 31/8 = 17/6 x 25/8 = 425/48 = 8 41/48 12/3 2¾ = 5/3 11/4 = 5/3 x 4/11 = 20/33 2½ x 41/3 1¼ = 5/2 x 13/3 5/4 = 5/2 x 13/3 x 4/5 = 260/30 = 26/3 = 8 2/3 SECTION 3 - APPROXIMATING & ESTIMATING Estimates and approximations bring 2 major benefits: 1. They enable you to check that the final answer is near to the figure that your estimate led you to expect. This is particularly valuable if you are unsure in the use of the keys on the calculator. 2. They can provide you with a ‘short cut’, by showing plainly that you do not need to do all the calculations (eg. when comparing figures in tables). Example 1 Calculate 51/73 of 300 steps i. Approximate 51/73 to 50/75 (move to figures that make easily handled fractions) ii. simplify 50/ 75 to 2/3 (by dividing top and bottom by 25) iii. Approximate answer is 2/3 300 i.e 200 iv. Calculator answer 209.59 (in fairly close range to 200, your approx. answer) Example 2 The following table shows the number of items sold in one year by the Beans Co. in each of its operating districts. Column Y shows the number of salespeople employed in each district. Column X Column Y Column Z District Number of Number of salespeople items sold SW 57 53,971 NW 38 64,562 Mid 31 21,123 SE 27 47,051 NE 23 42,510 Task 1. In which district was the highest number of items sold per salesperson? Task 2. In which district was the lowest number of items sold per salesperson? Steps: i. To make handling of figures more manageable, make approximations of the items sold figures. Approximation table District Salespersons Items sold (in thousands) SW 57 54 NW 38 64.5 Mid 31 21 SE 27 47 NE 23 42.5 Approximation and comparison can eliminate certain districts from the need to calculate accurately. Task 1. The highest average sales i. Mid and SE have similar numbers of salespeople, but Mid sold far fewer items. Hence Mid can be eliminated. ii. SW sold fewer items than NW, but had far more salespeople. Hence SW can be eliminated. iii. The districts ‘ left in ‘ for consideration are SE, NW, NE iv. Use a calculator to do the division, USING THE ACCURATE FIGURES, to find the averages of the 3 districts. SE 47,051/27 = 1742.6 NW 64,562/38 = 1699 NE 42,510/23 = 1848 Hence the highest average sales figures per salesperson was in the NE district. Task 2. The lowest average sales per person per district From your approximation table it is evident that Mid sold far fewer items than each of NW,SE,NE, despite having similar numbers of salespeople. It is not so clear as to how Mid compares with SW, so two calculations are desirable. SW 53,971/57 = 946.86 Mid 21,123/31 = 681 Hence Mid district had the lowest average number of items sold per salesperson SECTION 4 – AVERAGES There are several ways of expressing an average. The most common way is called a -mean . This is one value which is representative of all the numbers in a group. The mean is calculated by adding up all the numbers in a group, then dividing by how many numbers there are. Example 1 Find the average, or mean, of the following numbers: Mean = 2+6+4+8+5+5 = 30 = 5 6 6 Check your answer – is an answer of 5 representative of the numbers? Example 2 Find the average, or mean, of the following numbers: 1 3 4 2 1 20 Mean = 1+3+4+2+1+20 = 31 = 5.17 6 6 Check your answer – in this case, most of the numbers are less than 5 but the very high value of 20 pulls the mean upwards, so the answer is sensible. Example 3 In a test of numerical ability, students are tested in two groups. Which group has the higher average score? Group A Group B 3 7 15 6 8 10 9 11 12 19 13 20 3+15+8+9+12+13 7+6+10+11+19+20 6 6 = 60 = 73 6 6 = 10 = 12.17 Group B has the higher average score SECTION 5 - PERCENTAGES Percentage is one of three ways of expressing a value e.g. 17% has the same value as 17/100 or 0.17 It is recommended that, before using the calculator, you first understand, through mental calculation, the principles of layout of expressions and the functions of addition, subtraction, multiplication and division in fractions and decimals. Percentage and decimal - the relationship Examine the ‘meaning’ of the figure 425. 631. The position of each digit gives it its value. Regard each digit as being a member of a column i.e. a b c d e f 4 2 5 6 3 1 Column a expresses ‘whole HUNDREDS’. b expresses ‘whole TENS.. c expresses UNITS (ONES). d. expresses 1/10ths e. expresses 1/100ths F. expresses 1/1000ths. 1% is expressed as a fraction as 1/100. Hence, from the ‘column rule’, 1% is 1 in column e i.e 0.01 Try to memorise the following table. It shows how identical values are expressed in different forms – percentages, fractions and decimals 100% 100/100 1.00 10% 10/100 1/10 0.1 1% 1/100 0.01 0.1% 0.1/100 1/1000 0.001 Example Calculate 17% of 3/4 Give the answer as a percentage. i. Express 17% as 17/100 ii. 17% as 17/100 3/4 (note that ‘of’ becomes ‘‘ ) iii. The rule of multiplication of fractions applies. Multiply the top values (numerators), and multiply the bottom values (denominators) i.e (17 3 )/(100 4 ) = 51/400 iv. Approximate 51/400 to 50/400 v. Simplify 50/400 to 1/8 vi. Convert 1/8 to a percentage. The principle is that the 8 (denominator) has to be converted to 100 ( in this case by multiplying by 12.5). You treat the top figure in the same way (i.e 1 multiplied by 12.5 ) vii. You thus produce a fraction 12.5/100 (NB. you would not normally leave a fraction in this format). This indicates 12.5% as an APPROXIMATE ANSWER to the question. viii. Use the calculator to find the ACCURATE answer Answer 12.75% SECTION 6 - RATIO Ratio is crudely explained as the proportion in which something or some things are shared. i.e. an expression of how the shares of the total compare with each other. Example 1 Ann, Betty and Chris win a total of £1200 in a lottery. The money is shared according to how much each staked in the lottery. Ann is to receive 2 times as much as Chris. Betty is to receive 3 times as much as Chris. How much should each receive? You need to begin by establishing the total number of shares. Begin by allocating 1 share to Chris Ann will then have 2 shares (2 times Chris’s share) Betty will receive 3 shares (3 times Chris’s share) Thus the total prize is to be shared 6 ways (1+2+3) So one share will be £1200 divided by 6 i.e £200 Chris will receive £200, Ann £400 (2 times Chris’s share), and Betty £600 (3 times Chris’s share) SECTION 6 - RATIO Ratio is crudely explained as the proportion in which something or some things are shared. i.e. an expression of how the shares of the total compare with each other. Example 1 Ann, Betty and Chris win a total of £1200 in a lottery. The money is shared according to how much each staked in the lottery. Ann is to receive 2 times as much as Chris. Betty is to receive 3 times as much as Chris. How much should each receive? You need to begin by establishing the total number of shares. Begin by allocating 1 share to Chris Ann will then have 2 shares (2 times Chris’s share) Betty will receive 3 shares (3 times Chris’s share) Thus the total prize is to be shared 6 ways (1+2+3) So one share will be £1200 divided by 6 i.e £200 Chris will receive £200, Ann £400 (2 times Chris’s share), and Betty £600 (3 times Chris’s share) Check that the shares (£200 +£400 + £600) total £1200 Different phraseology of this question could be..... £1200 is to be shared out between Chris, Ann and Betty, in the RATIO of 1:2:3 respectively. How much will each receive? Example 2 A school collected money for a new laboratory, using three methods, raffle, sponsored walk and fete. The total collected was £5200 in the ratio of 5:2:3 for each method in the order - raffle, walk, fete. How much did each method raise? i. 5:2:3 expresses the proportions (‘shares’) ii. The total number of shares is 5+2+3 i.e. 10 iii. The total collected was £5200 iv. Each share was £5200/10 i.e. £520 v. The raffle raised 5 ‘shares’ of £520 i.e. £2600 The walk raised 2 ‘shares’ of £520 i.e. £1040 The fete raised 3 ‘shares’ of £520 i.e. £1560 vi. CHECK the total by addition i.e. £5200 ANSWERS SECTION 1 – DECIMALS Question 2 decimal places 2 significant figures 1 10.13 10 2 15.32 15 3 15.52 16 4 164.67 160 5 8.80 8.8 6 1.80 1.8 7 161.33 160 8 1.02 1.0 9 25.68 26 10 10.80 11 11 22.22 22 12 318.75 320 13 51.21 51 14 2.47 2.5 15 19.53 20 16 2.33 2.3 17 83.33 83 18 106.38 110 SECTION 2 – FRACTIONS 1. 11/15 2. 27/40 3. 1 7/24 = 31/24 4. 58/99 5. 26/63 6. 13/24 7. 7/8 8. 1 7/12 = 19/12 9. 9 27/40 = 387/40 10. 8/15 11. 8/27 12 7/15 13. 4/3 14. 5/22 15. 16/21 16. 7 7/8 = 63/8 17. 11 11/35 = 396/35 18. 16 8/27 = 440/27 19. 2 1/57 = 115/57 20. 25/62 21. 10/13 22. 6 ¾ = 27/4 23. 19 8/21 = 407/21 24. 14 SECTION 4 – AVERAGES 1. 4.43 2. 59.11 3. 7 4. 16.5 5. 112.8 6. Group A = 11.9, Group B = 11.6 so the answer is Group A (just!) 7. Overall average = 122/30 = 4.067. Day 1 average = 41/10 = 4.1. Day 2 average = 48/10 = 4.8 Day 3 average = 33/10 = 3.3, so Day 2 has the worst overall average. On Day1, 2 students were more that 5 minutes late, Day2 = 5 students and Day 3 = 1 student so Day 2 is also the day on which most students were more that 5 minutes late. SECTION 5 – PERCENTAGES i. £16 v. 3.15 ix. 58% ii. 2.5% vi. £243 x.a 20,781 iii. 5/16 vii. 0.6% x.b 3958 iv. 5 viii. 0.0025 x.c 3% SECTION 6 – RATIOS i. 7,000, 7,000, 14,000, 21,000, 21,000 ii. Alan 40, Ben 80, Chris 240 and Doug 120
Posted on: Sat, 29 Jun 2013 11:36:33 +0000
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