Page 73 - Start Up Mathematics_3

Example 7: There are 28 mangoes in a box. How many mangoes will be there in
6 such boxes?

Solution: Number of mangoes = 28 × 6
Quick Tip
To estimate the product, round off 28
to the nearest 10. We have not rounded
off 6 as it is a single-
28 rounded off = 30 digit number and is
easy to multiply.
Multiply the rounded off number by 6.
30 × 6 = 180

So, the product 28 × 6 will be approximately 180.
Actual product: 28 × 6 = 168

H T O

4 2 8

× 6

1 6 8

Example 8: Estimate 45 × 22 = ?

Solution: To estimate the product, round off 45 and 22 to the
nearest 10. H T O
45 rounded off = 50 22 rounded off = 20 4 5

Now multiply the rounded off numbers. × 2 2

50 × 20 = 1000 9 0
So, the product 45 × 22 will be approximately 1000. + 9 0 0

Actual product: 45 × 22 = 990 9 9 0

Solving Word Problems

Example 9: Humaira purchased 15 colour boxes to give as return
gift for her birthday party. If one colour box costs H T O
` 23, how much did Humaira pay in all?
2 3
Solution: Number of colour boxes = 15 × 1 5

Cost of 1 colour box = ` 23
Cost of 15 colour boxes = ` 23 × 15 1 1 5

= ` 345 + 2 3 0

Humaira paid ` 345 in all. 3 4 5

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