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This problem trains for: SAT-I, AMC-8, GMAT, AMC-10.

If x varies directly with d2 and indirectly with p2 what happens to x if p/d is doubled?

The dependency of x on d and p is of the form:

where k is some real constant.

We can rewrite the equality above as:

If the ratio p/d doubles:

x is quartered.