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2 Find the number of divisors of 1080 excluding the divisors which are perfect squares.
A. 28
B. 30
C. 29
D. 31
See Answer & Explanation Lets Discuss
Correct answer is : A
Explanation

1080=23 x 33 x 51

So, Number of divisors/factors = 4 x 4 x 2 = 32
Out of all the factors  1, 4(22), 9(33) and 36 (9 x 4) are perfect Squares.

So the answer is 32-4 = 28.

 

Anand 6/4/2014 10:34:27 PM

how do we easily find 1, 4, 9 and 36 are the perfect squares? Does it have any logic?

dhivya 7/31/2014 10:30:02 PM

pls explain this logic.? i did'nt know why 36 come.

sonu 10/3/2014 12:39:11 AM

i am not clear form this answer because i am not understood this concept........please reply step by step.

 

Dishi Gupta 11/28/2014 8:05:58 PM

1080=2^3 x 3^3 x 5^1

we have to guess the factors which are perfect squares from above factors...

i.e.1, 4(2^2), 9(3^3) and 36 (2^2*3^3) are perfect Squares from above factors.

36 (2^2*3^3)-this is taken by breaking the factors of 1080 for getting a perfect square... This is how 36 is taken.

So the answer is 32-4 = 28.

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