97
Subtracting fractions with regrouping
Textbook: Part 3, lesson 97, pp. 81–83
GoalSubtracting with regrouping: when the fraction part of the first number is smaller than that of the second.
New words
with regrouping · birlikdan o‘tibminuend · kamayuvchisubtrahend · ayriluvchione whole · butun birlik
Explanation
If the fraction part of the first number is smaller than that of the second, take one unit from its whole part, change it into shares and add it to the fraction part. For example 5 2/7 − 1 5/7: 5 2/7 = 4 9/7, so 4 9/7 − 1 5/7 = 3 4/7. Check: 3 4/7 + 1 5/7 = 5 2/7.
Worked examples
8 3/10 − 2 7/10: 8 3/10 = 7 13/10; 7 13/10 − 2 7/10 = 5 6/10.
6 1/4 − 3 3/4: 6 1/4 = 5 5/4; 5 5/4 − 3 3/4 = 2 2/4.
Class activity
“Borrowing”: each pair takes a subtraction card and subtracts with regrouping using whole circles, then checks by adding.
Practice
1
Work out 5 2/7 − 1 5/7.
3 4/7
2
Work out 8 3/10 − 2 7/10.
5 6/10
3
Work out 6 1/4 − 3 3/4.
2 2/4
4
A board was 4 2/5 m long and 1 4/5 m was cut off. How many metres are left?
2 3/5
5
Solve the equation: x + 2 7/9 = 5 4/9.
2 6/9