The LCM of two positive no’s is 168 and their product is 504. what is the difference in their squares?

A. 175

B. 216

C. 9

D. 135

Answer : D. 135…

504 = 2*2*2*3*3*7 = 8*3*3*7 = 24*21
168 = 2*2*2*3*7
It means 3 will come in both the numbers as 3 is coming once in LCM but coming as 9 in product.
so possible numbers are 24 and 21.

Now the difference of the square of these numbers is a^2-b^2 = (a+b)(a-b)
= (24+21)(24-21)
= 45(3)
= 135

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