swerve wrote:A car traveled 60 mph from Belnap to Lincoln and 50 mph from Lincoln to Belnap. If the whole trip was 660 miles, how long did the round trip take?

A. 6 hours
B. 11 hours
C. 12.1 hours
D. 13.2 hours
E. 24.2 hours

The OA is C.

Please, can any expert explain this PS question for me? I'm not sure why that is the correct answer. Thanks.

Here's a quick solution.

Let's see what happens if the car travels at the SAME SPEED for the entire 660 miles.

Time = distance/speed

IF the car traveled 60 mph for the entire 660 miles, then...
Travel time = 660/60 = 11 hours

Since the car traveled at a SLOWER speed of 50 mph for half of the trip, we can conclude that the entire trip took longer than 11 hours to complete
ELIMINATE A and B

IF the car traveled 50 mph for the entire 660 miles, then...
Travel time = 660/50 = 66/5 = 13.2 hours

ASIDE: Here's a brief video explaining a very fast way to quickly divide ANY number by 5 in your head: https://www.gmatprepnow.com/module/gene ... video/1112

Since the car traveled at a FASTER speed of 60 mph for half of the trip, we can conclude that the entire trip took less than 13.2 hours to complete
ELIMINATE D and E

By the process of elimination, the correct answer must be C

Cheers,
Brent

swerve wrote:A car traveled 60 mph from Belnap to Lincoln and 50 mph from Lincoln to Belnap. If the whole trip was 660 miles, how long did the round trip take?

A. 6 hours
B. 11 hours
C. 12.1 hours
D. 13.2 hours
E. 24.2 hours

The OA is C.

Please, can any expert explain this PS question for me? I'm not sure why that is the correct answer. Thanks.

The time for the entire trip was:

330/60 + 330/50 = 33/6 + 33/5 = 11/2 + 33/5 = 55/10 + 66/10 = 121/10 = 12.1 hours

Answer: C