88
Adding and subtracting fractions
Textbook: Part 3, lesson 88, pp. 54–56
GoalAdding and subtracting fractions with the same denominator: add or subtract the numerators, keep the denominator.
New words
addition · qo‘shishsubtraction · ayirishsame denominator · bir xil maxrajsum · yig‘indi
Explanation
To add fractions with the same denominator, add the numerators and keep the denominator: 3/8 + 2/8 = 5/8. To subtract, subtract the second numerator from the first and keep the denominator: 9/10 − 4/10 = 5/10. The shares are the same size, so we add or subtract how many there are. If the sum is an improper fraction, it can be written as a mixed number.
Worked examples
2/9 + 5/9 = (2 + 5)/9 = 7/9. 11/12 − 7/12 = (11 − 7)/12 = 4/12.
5/8 + 6/8 = 11/8 = 1 3/8 (11 : 8 = 1 remainder 3).
Class activity
“Jumping on the ray”: mark 12 equal steps from 0 to 1. A child jumps 3/12, then another 4/12 and writes where they land. Then they jump back to subtract.
Practice
1
Work out 2/9 + 5/9.
7/9
2
Work out 11/12 − 7/12.
4/12
3
Work out 5/8 + 6/8 and also write the result as a mixed number.
11/8 = 1 3/8
4
Guests ate 3/10 of the samsas Mum baked and the family ate 4/10. What part of the samsas is left?
3/10
5
Solve the equation: x + 3/7 = 6/7.
3/7