Mathematics Express as Fractions

Lesson Objectives The aim of this powerpoint is to help you… to express one value as a fraction of another

Express as a Fraction To express one value as a fraction of another you must first ensure that BOTH values have the same type of units. If they don’t you will have to convert one of them. Once they both have the same type of units, write the first value over the second value. Make sure the fraction is valid (i.e. doesn’t contain fractions or decimals within the fraction) by finding an equivalent fraction If the question asks for the answer in its simplest terms remember to cancel the fraction down if possible.

Example 1 Express 50p as a fraction of £2. First convert 50p into pounds OR convert £2 into pence….. (£2 = 200p) Now we have express 50p as a fraction of 200p 50 200 ÷50 1 ÷50 4 ≡

Example 2 What fraction of 3kg is 1600g? First convert 1600g into kg OR convert 3kg into grams….. (3kg = 3000g) Now we need 1600g as a fraction of 3000g 1600 3000 ÷200 8 ÷200 15 ≡

Example 3 Note: She got 20 – 13 = 7 wrong In a test of 20 questions, Cara got 13 questions correct. What fraction of the questions did she get wrong? Note: She got 20 – 13 = 7 wrong We have to express 7 as a fraction of 20 7 20

Quick Practice For each of the following, express the first value as a fraction of the second value, giving your answer in its simplest terms. A 20p, £5 D 34mm, 5cm B 15cm, 1m E 30p, £1 C 16g, 80g F 1200m, 4km Work out your answers before clicking on to the next slide.

Answers A 20p, £5  20p, 500p 20 500 B 15cm, 1m  15cm, 100cm 15 100 C 16g, 80g 16 80 = 1 25 = 1 25 Both numbers end in 0 so divide them BOTH by 10 Now both numbers are even so divide them BOTH by 2 = 3 20 Both numbers end in 5 and 0 so divide them BOTH by 5 = 8 40 = 4 20 = 2 10 = 1 5 You can divide by 2 several times! Both numbers are even so divide them BOTH by 2

Answers (cont’d) 17 3 3 25 10 12 40 10 D 34mm, 5cm  34mm, 50mm 34 50 E 30p, £1  30p, 100p 30 100 F 1200m, 4km  1200m, 4000m 1200 4000 = 17 25 Both numbers are even so divide them BOTH by 2 = 3 10 Both numbers end in 0 so divide them BOTH by 10 = 12 40 = 3 10 Both numbers are in the 4x table so divide them BOTH by 4 Both numbers end in 00 so divide them BOTH by 100

What next? Print out the notes called Frac7. Read them and make sure you answer any questions If you need more practice, try the worksheet called ExpFrac-S1.xlsx. Now move on to the Frac-8 powerpoint