Question

Estimate the following products using general rule:
$578 \times 161$
$5281 \times 3491$
$1291 \times 592$
$9250 \times 29$

Answer 1

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Here is the solution:

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A general rule for estimation: Unless otherwise stated, we always round each number to one significant figure.

578 x 161

578 is between 500 and 600. It is closer to 600 than 500 ⇒ 576 ≈ 600

161 is between 100 and 200. It is closer to 200 than 100 ⇒ 161 = 200

578 x 161 = 600 x 200 = 120,000

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5281 x 3491

5281 is between 5000 and 6000. It is closer to 5000 than 6000 ⇒ 5281 ≈ 5000

3491 is between 3000 and 4000. It is closer to 3000 than 4000 ⇒ 3491 = 3000

5281 x 3491 = 5000 x 3000 = 15,000,000

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1291 x 592

1291 is between 1000 and 2000. It is closer to 1000 than 2000 ⇒ 1291 ≈ 1000

592 is between 500 and 600. It is closer to 600 than 500 ⇒ 592 = 600

1291 x 592 = 1000 x 600 = 600,000

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9250 x 29

9250 is between 9000 and 10000. It is closer to 9000 than 10000 ⇒ 9250 ≈ 9000

29 is between 320 and 30. It is closer to 30 than 20  ⇒ 29 = 30

9250 x 29 = 9000 x 30 = 270,000