Fractions with the Same Denominator
Primary 4 · Mathematics
Fractions with the Same Denominator
Lesson 3 of 5
30 min
Let's begin
Mutesi's family has a small field. In the rainy season they plant beans on 310 of the field and maize on 410 of it. How much of the field is planted, and how much is still empty? Adding fractions will tell us.
When the denominators are the same, the pieces are the same size. So just count the pieces: add the numerators and keep the denominator.
28 + 38 = 58: two eighths and three more eighths make five eighths.
Watch out! Never add the denominators. 28 + 38 is not 516. The pieces are still eighths; you just have more of them.
Subtract the numerators and keep the denominator. Then simplify if you can.
710 − 310 = 410 = 25.
When the numerator and the denominator are the same, the fraction is one whole: 88 = 1, and 35 + 25 = 55 = 1.
To take a fraction away from 1, write 1 as a fraction with the same denominator first: 1 − 38 = 88 − 38 = 58.
Back to Mutesi's field. Planted: 310 + 410 = 710 of the field. Empty: 1 − 710 = 1010 − 710 = 310 of the field.
Tip
The bottom stays, the top plays. When the denominators match, add or subtract only the numerators. The denominator stays the same.
Work each one in your exercise book first. Then tap Show answer to check.
37 + 27
Answer: 57
59 − 19
Answer: 49
16 + 36
Answer: 46, which simplifies to 23
1 − 45
Answer: 15, because 55 − 45 = 15
Keza read 312 of her storybook on Monday and 512 on Tuesday. What fraction has she read? What fraction is left?
Answer: She has read 812 = 23. 412 = 13 is left.
What you learned today
Sources and credits
The stories, Rwandan worked examples, diagrams and practice questions were written by Ganzaa.
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