The quantity n varies jointly with the product of z and the square of the sum of x and y When x is equal to 2 , y is equal to 1 , and z is equal to 3 , n is equal to 18 What is the constant of variation?

Joint variation with the product of z and (x + y)² means n = k z(x + y)², where k is the constant of variation. Substitute x = 2, y = 1, z = 3, and n = 18: 18 = k · 3 · (2 + 1)² = 27k. Therefore, k = 18/27 = 2/3, which is choice A, “2 thirds.”

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