GMATBLACKBELT wrote:

eschn3am wrote:

You can right out the formula (ala Walker

) or you can pick simple numbers and do it that way. I prefer the number approach:

Let X = 60

60 miles at 60mph = 1 hour for trip at constant speed

Other trip would be 55 miles at 60mph + 5 miles at 30mph.

55 miles at 60 = 55 minutes

5 miles at 30 = 10 minutes

Total Trip: 65 minutes

65/60 = 13/12

The travel time is 1/12 greater which is equal to 8.33%

Of the answer choices only E is equal to 8.33% because 500/60 = 8 (to get to 480) and then 20/60 = 1/3.

Answer E I did this same approach, but I said x=120.

For E 500/120 doesnt work. I still get 2.16667-2.083333 = .08333....

hrmmmmmm ?_?

It will work for any number X. Let's work through it using 120 because that's easy to work with.

Let X = 120

120 miles at 60mph = 2 hours for trip at constant speed (or 120 minutes)

Other trip would be 115 miles at 60mph + 5 miles at 30mph

115 miles at 60 = 115 minutes

5 miles at 30 = 10 minutes

Total Trip: 125 minutes

125/120=25/24

The travel time is 1/24 greater, which is equal to 4.1667% or 4 + 1/6

500/120 = 4 + 20/120 = 4+1/6 = 4.1667%

Answer E