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Question: If N = 7<sup>p+4</sup>.5<sup>q</sup>.2<sup>3</sup> is a perfect cube, where 'p' and 'q' are positive...

If N = 7p+4.5q.23 is a perfect cube, where 'p' and 'q' are positive integers, the smallest possible value of 'p + q' is-

A

5

B

2

C

8

D

6

Answer

5

Explanation

Solution

N = 7p + 4 . 5q.23 is perfect cube.

7, 5, 2 has no common factor except '1'.

Least value of 'q' is 3 for which 5q is cube.

Least value of 'p + 4' is '6' for which 7p+4 is cube.

p + 4 = 6 Ž p = 2

\ Least value of p + q = 2 + 3 = 5.