If p and r are integers, and p^2 = 28r, then r must be divisible by which of the following?  Choose the correct answer
A) 2  B) 4  C) 5  D) 7  E) 14
Solution: for p to be an int 28 r must be whole square of a number.   28r= 7*2*2*r   to make it whole square we need 7   so r can must be divisible by 7y where y is itself a whole square.   so Answer is 7
<result>D</result>
If p and r are integers, and p^2 = 28r, then r must be divisible by which of the following?