Find the smallest number \(y\) such that \(y×162\) is a perfect cube.
2017
Find the smallest number \(y\) such that \(y×162\) is a perfect cube.
- A.
24
- B.
27
- C.
32
- D.
36
Attempted by 110 students.
Show answer & explanation
Correct answer: D
Answer: 36
Prime-factorize the given number: 162 = 2^1 × 3^4.
For a product to be a perfect cube, each prime's exponent must be a multiple of 3. Current exponents are: 2 → 1, 3 → 4.
Make each exponent a multiple of 3 by multiplying by the minimal additional powers: increase exponent of 2 from 1 to 3 (need 2 more factors of 2) and increase exponent of 3 from 4 to 6 (need 2 more factors of 3).
Thus y = 2^2 × 3^2 = 4 × 9 = 36.
Check: 162 × 36 = 2^3 × 3^6 = (2 × 3^2)^3 = 18^3, so the product is indeed a perfect cube.
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