atalpanditgmat wrote:

A train travels at the rate of 10 miles/hr for the first hour of a trip, at 20 miles/hr for the second hour, at 30 miles/hr for the third hour and so on. How many hours will it take the train to complete a 450-mile journey? Assume that the train makes no intermediate stops.

A. 8

B. 8.5

C. 9

D. 9.5

E. 10

First check the answer choices (

ALWAYS check the answer choice before deciding on an approach to a question)

We see that all answer choices are between 8 hours and 10 hours.

So, let's test the answer choices, starting with 8 hours, and then go from there (if need be).

A) 8 hours

Distance = (rate)(time)

So, the train travels 10 miles in the 1st hour, 20 miles in the 2nd hour, 30 miles in the 3rd hour, . . . . . 80 miles in the 8th hour

So, TOTAL distance traveled = 10 + 20 + 30 + 40 + 50 + 60 + 70 + 80 =

360 milesWe want the train to travel 450 miles, so we need to keep going

ASIDE: We know that the train travels

90 miles in the 9th hour.

So, AFTER 9 hours the distance the train has traveled =

360 miles +

90 miles = 450 VOILA!!

Answer: C

Cheers,

Brent

_________________

Brent Hanneson – Founder of gmatprepnow.com