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Example 19: Subtract 73 from 90.

Solution: Round off 73 to 70. (73 – 70 = 3)
Subtract 70 from 90.

90 – 70 = 20
As we subtracted 3 less than 73, correct the answer by subtracting 3 from 20.

So, 90 – 73 = 17.

Exercise 3.6

Subtract the given numbers mentally using any two suitable methods.

(a) 80 – 47 (b) 98 – 92 (c) 89 – 73

Review Exercise

1. Subtract the given numbers.

(a) H T O (b) H T O (c) H T O

3 9 6 6 8 7 9 6 5
– 7 5 – 3 9 – 4 8

(d) H T O (e) H T O (f) H T O
1 6 3 9 3 6 8 6 4

– 4 1 – 5 0 8 – 5 1 2

(g) H T O (h) H T O (i) H T O
4 3 5 9 5 8 6 2 1

– 2 1 0 – 2 2 7 – 1 0 6

(j) H T O (k) H T O (l) H T O

3 7 9 8 6 3 4 3 2

– 2 8 0 – 7 1 8 – 1 9 2

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