Which of the following is the closest approximation to 73 \times 239 7.2 + 15.7?

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PS · Problem Solving

705-805

Roots

Which of the following is the closest approximation to $\frac{\sqrt{73} \times \sqrt{239}}{\sqrt{7.2} + \sqrt{15.7}}$ ?

Answer Choices

Correct answer marked below

A

10

B

15

20

Correct

D

25

E

30

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Explanation

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Official Explanation

Official

Approximate to all to next higher squares:

- 73 to 81

- 239 to 256

- 7.2 to 9

- 15.7 to 16…

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What this question tests

What it tests

Your handling of square and higher roots, including simplifying radicals.

Common trap

Forgetting the ± when taking a square root to solve an equation, or assuming √(a²) = a.

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Which of the following is the closest approximation to 73×2397.2+15.7\frac{\sqrt{73} \times \sqrt{239}}{\sqrt{7.2} + \sqrt{15.7}}7.2​+15.7​73​×239​​?