PR problem - tires

Cost of new tires 180 per tire. so total cost is 180 X 4.
But they last for 4 yrs.

Hence cost of 4 new tires per year is 180X4/4 = 180 / year

Cost of repairing is 40 per tire. so total cost is 40 X 4 = 160
But they last for 1 year.

Hence cost of 4 repaired tires per year is 160 / year.

So it cost 20$ more for the new tires.

percentage increase will be 20X100/160 = 12.5%

Tires of a certain brand, when purchased new, last for four years. A customer can choose to purchase the new tires at a cost of $180 per tire or can have his current tires repaired at a cost of $40 per tire, a repair that will make the current tires last for one additional year. The average cost per year of the new tires is what percent greater than the cost of repairing the current tires?

A. 8%
B. 10%
C. 12.5%
D. 16.7%
E. 25%

Cost of 1 brand new tire = $180..However, the costs spread across 4 years effectively cost 180/4 = $45 a year...

Current tires can be repaired at a cost of $40 per tire and the life increased by 1 year....

Hence % = 45-40 / 40 * 100
= 5/40 * 100
= 100/8 = 12.5%

Yup OA is indeed C.

PR has some calculations based on 4 tires -- which cannot be assumed without knowing where the tires are going to be used - a car, a bike or a
freaking 18 wheeler !!

Since this is a percentage problem, I guess its ok to use 4 or any number
as the numerator and denominator would cancel out but if it weren't
it would be a bummer.