Operations on Fractions
Primary 6 · Mathematics
Operations on Fractions
Lesson 2 of 6
30 min
Let's begin
Every morning Mugisha drinks 34 of a litre of milk from the family cow. His father asks, “How much milk do you drink in 5 days?” Mugisha starts adding 34 five times. Is there a faster way?
Multiplication is repeated addition, even with fractions:
5 × 34 = 34 + 34 + 34 + 34 + 34 = 154 = 3 34 litres.
The quick way: multiply the whole number by the numerator and keep the denominator. You can think of 5 as 51: 51 × 34 = 154.
In maths, the word “of” means multiply. 25 of 3 000 Frw means 25 × 3 000.
Worked example
Keza saves 25 of her 3 000 Frw pocket money. How much does she save?
Dividing first keeps the numbers small.
The order does not matter: 38 × 40 = 40 × 38. One eighth of 40 is 5, so three eighths is 15. 38 × 40 = 15.
Worked example
A moto ride from Kimironko to the city centre costs 1 200 Frw. On a promotion day, riders pay 34 of the fare. What does a rider pay?
56 × 18: divide 18 by 6 first to get 3, then 5 × 3 = 15. This is quicker than working out 906.
Worked example
2 12 × 6
Tip
“Of” means times. Divide by the bottom, multiply by the top. To find 34 of something, find one quarter first, then take three of them.
Work each one in your exercise book first, then tap Show answer to check.
4 × 29
Answer: 89. Multiply the whole number by the numerator.
Find 35 of 2 500 Frw.
Answer: 2 500 ÷ 5 = 500, then 500 × 3 = 1 500 Frw.
710 × 60
Answer: 42.
A bag of beans weighs 1 14 kg. What do 8 bags weigh?
Answer: 54 × 8 = 404 = 10 kg.
What you learned today
Sources and credits
The stories, Rwandan worked examples and practice questions were written by Ganzaa.
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