A quantity b varies jointly with c and d and inversely with f When c is 4 , d is 9 , and f is 6 , b is 18 What is the constant of variation?

Since b varies jointly with c and d and inversely with f, write b = kcd/f, where k is the constant of variation. Substitute b = 18, c = 4, d = 9, and f = 6: 18 = k(4)(9)/6 = 6k, so k = 3. The constant of variation is 3, choice C.

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