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If p varies inversely as the cube of q and q varies directly as the square of r, what ...

If p varies inversely as the cube of q and q varies directly as the square of r, what is the relationship between p and r?
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  • A P varies directly as r3
  • B P varies inversely as r6
  • C P varies inversely as 6√P
  • D P varies directly as r6
Correct Answer: Option C
Explanation:
P ∝ 1/q3
P = K/q3
q3 = K/P
q = K/p[sup]1/[sub]3[/sup][/sub]
But q ∝ r2
q = Kr2K/p[sup]1/[sub]3[/sup][/sub] = Kr2
r2 = K/p[sup]1/[sub]3[/sup][/sub] x 1/K
r2 = 1/p[sup]1/[sub]3[/sup][/sub]
r = (1/p[sup]1/[sub]3[/sup][/sub])2
r = 1/p[sup]1/[sub]6[/sup][/sub]
r ∝ 1/p[sup]1/[sub]6[/sup][/sub]
∴ r varies inversely as 6√P

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