Question

Suppose that the increase in the fee from $8 to $16 reduces travel time in the central city from 30 minutes down to 20 minutes. what is the percentage change in the total cost of driving in central london?

Answer 1

With regards to the change in total cost driving to London, the price doubled from $8 to $16. So the total change in cost was $8 or 50% price change. However, though there is an increase in price, the travel time goes down, which is optimal in heavy traffic. 

Answer 2

If your choices are the following:
a) $20
b) $12
c) $10
d) $8
e) $5

Then the answer is letter e. 16-8 = 8 so this is the difference between the 10 minutes. So this means 8 is the best answer.