Question

Designer dolls, inc found that the number of dolls sold, n, varies directly as their advertising budget, a, and inversely as the price of each doll, p. designer dolls, inc. sold 12,000 dolls when $50,000 was spent on advertising and the price of the doll was set at $50. determine te number of dolls sold when the amount spent on advertising is increased to $65,000.
a. 15,600
b. 1,300
c. 2,880
d. 15,120

Answer 1

We are given the statement that the number of dolls, n is directly as their advertising budget, a, and inversely as the price of each doll, p. In this case, we express it to a formula : n = ka /p where k is the constant of proportionality. applying the law of proportion, 

n1*p1/a1 = n2*p2/a2
12,000*$50/$50,000 = n2* $50 / ($50000 + $65,000)
n2 = 27,600 dolls