RemeliaMaths Year 3 Fractions, decimals & %
Year 3 adding and subtracting fractions
The objective: Add and subtract fractions with the same denominator within one whole.
The explanation, example and questions are the ones Remelia uses in the app; the questions are not taken from any test paper.
The idea
When the denominators match, the pieces are the same size, so you can just count them. Add the tops and leave the bottom alone.
How to do it
- Check the denominators are the same.
- Add or subtract the numerators.
- Keep the denominator exactly as it was.
A worked example
2/7 + 3/7 = 5/7. The sevenths did not change size, there are just more of them.
Watch for
Adding the bottoms too. 1/5 + 2/5 = 3/5, never 3/10.
Try four questions
-
Priya eats 1/7 of a cake.
What fraction of the cake is left?
- A 8/9
- B 7/8
- C 13/14
- D 6/7
Show the answer to question 1
Answer: D · 6/7
Why:
The whole cake is 7/7. 7/7 − 1/7 = 6/7.
-
4/9 + 4/9 = ?
Write your answer as a fraction, like 3/8.
Show the answer to question 2
Answer: 8/9 · accept equivalent fractions
Why:
The denominators are the same, so add the numerators only: 4 + 4 = 8, giving 8/9. The denominator never changes.
-
Leo works out 3/6 + 1/6 and writes 4/12.
What mistake, if any, did Leo make?
- A They multiplied the numerators
- B They made no mistake
- C They added the denominators as well as the numerators
- D They took the numerators away instead of adding them
Show the answer to question 3
Answer: C · They added the denominators as well as the numerators
Why:
3/6 + 1/6 = 4/6: add the numerators, and keep the denominator.
Leo got 3 + 1 = 4 right on top, but added 6 + 6 = 12 underneath too.
-
Maya eats 2/4 of a bar of chocolate.
What fraction of the bar is left?
Show the answer to question 4
Answer: 2/4 (also accept 1/2) · accept equivalent fractions
Why:
The whole bar is 4/4. 4/4 − 2/4 = 2/4.
Answers
- 1. D · 6/7
- 2. 8/9 · accept equivalent fractions
- 3. C · They added the denominators as well as the numerators
- 4. 2/4 (also accept 1/2) · accept equivalent fractions
The mistakes Remelia names
When a wrong answer to a question like these matches one of these mistakes, the app says what the child seems to have done before they try again.
- Question 1, the answer 1/7: That is the part given away. The question asks how many are left, so take it away from the whole.
- Question 2, the answer 8/18: It looks as if you added the denominators too. When the denominators are the same, add only the numerators. The denominator stays the same.