If y = 7.2 when x = 10, what is the value of x when y = 20? (y varies inversely as the square of x.)

a. 6
b. 10
c. 14.4
d. 20

 The correct option is (A) 6..

Step-by-step explanation:  Given that y varies inversely as the square of x and y = 7.2 when x = 10.

we are to find the value of x when y = 20.

Since y varies inversely as the square of x, so we have

When y = 7.2 and x = 10, then we get

So, we get the relation as follows :

When y = 20, then from equation (i), we get

Thus, the required value of x is 6 or -6. Since x = -6 is not in the options, so option (A) is CORRECT.