Page 70 - Start Up Mathematics_4
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Estimating Product of Two Numbers
Estimating product means finding an approximate value of the product of two numbers by
rounding them to the nearest 10, 100, 1,000, and so on.
Example 8: Estimate the product of 48 and 72. Check with the actual value.
Solution: 5
1 5 0
4 8 → (Rounded off to the nearest 10)
× 7 2 → × 7 0 (Rounded off to the nearest 10)
9 6 3 5 0 0
1 ↓
3 3 6 0 Estimated value
3 4 5 6
↓
Actual value
So, the estimated product is 3,500.
Example 9: Estimate the product of 265 and 138 by rounding off the numbers to the
nearest 100.
Solution: 2 6 5 → 3 0 0
1 3 8 → × 1 0 0
3 0 0 0 0
So, the estimated product is 30,000.
EXERCISE 5.7
1. Estimate the product by rounding off the numbers to the nearest 10.
(a) 49 × 83 (b) 76 × 52 (c) 98 × 65 (d) 114 × 28
(e) 237 × 41 (f) 108 × 175 (g) 65 × 99 (h) 82 × 76
2. Estimate the product by rounding off the numbers to the nearest 100.
(a) 361 × 226 (b) 472 × 594 (c) 716 × 119 (d) 2,841 × 154
(e) 3,075 × 216 (f) 8,792 × 361 (g) 453 × 249 (h) 728 × 395
Multiplication Tricks
Multiplying ‘teens’ Know More
Look at the following example to multiply numbers whose
names end with ‘teens’. 1,089 × 9 = 9,801 which is
exactly the reverse of 1,089.
Example 10: 13 × 15 = ?
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