Operations on Fractions
Primary 6 · Mathematics
Operations on Fractions
Lesson 1 of 6
35 min
Let's begin
Umutoni goes to Kimironko market with her mother. They buy 34 kg of beans and 12 kg of rice. “How much do the bags weigh together?” asks her mother. Before we multiply and divide fractions in this unit, let us sharpen the tools we already have.
Multiply or divide the numerator and the denominator by the same number, and the fraction keeps its value: 23 = 46 = 812.
To write a fraction in its simplest form, divide the top and bottom by their GCF (you met the GCF in Unit 3).
Worked example
Simplify 1824. GCF(18, 24) = 6. 18 ÷ 6 = 3 and 24 ÷ 6 = 4, so 1824 = 34.
You can only add or subtract fractions when they are cut into the same size pieces, that is, when the denominators are the same.
Worked example 1
Umutoni's shopping: 34 kg + 12 kg.
Worked example 2
34 + 16
Worked example 3
56 − 14
Worked example 4
3 12 − 1 23
Explore: the Fractions: Equality simulation lets you build fractions from pieces and see which ones are equal.
Tip
Never add the bottoms. The denominator is the NAME of the piece (quarters, sixths). 1 quarter + 2 quarters = 3 quarters, just as 1 goat + 2 goats = 3 goats, not 3 “double goats”.
Work each one in your exercise book first, then tap Show answer to check.
Write 3045 in its simplest form.
Answer: 23. Divide top and bottom by GCF(30, 45) = 15.
Write 3 25 as an improper fraction.
Answer: 175. (3 × 5 + 2 = 17)
23 + 14
Answer: 812 + 312 = 1112.
78 − 12
Answer: 78 − 48 = 38.
Keza walks 1 34 km to school and 2 12 km to the market. How far does she walk altogether?
Answer: 74 + 52 = 74 + 104 = 174 = 4 14 km.
What you learned today
Sources and credits
The stories, Rwandan worked examples and practice questions were written by Ganzaa.
Quick check
Write 24/36 in its simplest form.
