Since none of the variables is determined in the problem, their values can be selected at random.
Remember that m and p are expressed as dollars and n and q are expressed as cents. Let m = 10, n = 200, p = 20, q = 100. Then agency A charges $10 per day plus $2 per mile, and agency B charges $20 per day plus $1 per mile. (Notice that the agency with the higher daily fee must offer a lower mileage rate; otherwise, the prices will never be the same.)
For a two-day rental, agency A charges $20 plus $2/mile, and agency B charges $40 plus $1/mile. To solve algebraically, let x be the number of miles driven:
20 + 2x = 40 + 1x
x = 20
20 is the target value. Find a match in the answer choices:
(A) 100(–10)/(–100) = 10 miles.
(B) 200(10)/(100) = 20 miles.
(C) 50(–10)/(–100) = 5 miles.
(D) 2(10)/(100) = 0.2 mile.
(E) –10/(2× –100) = 0.05 mile.
Only choice B gives the desired figure of 20 miles.
This question can also be answered algebraically. One cent is equal to 0.01 dollars. Therefore, rental agency A charges $m per day plus $0.01n per mile, and rental agency B charges $p per day plus $0.01q per mile.
Let x be the number of miles at which the fees are equal, for two days’ rental:
2m + (0.01n)x = 2p + (0.01q)x
2m – 2p = 0.01qx – 0.01nx
2(m – p) = 0.01x(q – n)
x=200(p - m)/(n - q)
The correct answer is B.