DensetsuNo wrote:

A car traveled 65% of the way from Town A to Town B at an average speed of 65 mph.

The car traveled at an average speed of v mph for the remaining part of the trip.

The average speed for the entire trip was 50 mph. What is v in mph?

(A) 65

(B) 50

(C) 45

(D) 40

(E) 35

Source: Nova's GMAT Math Prep

Kudos for nice answers.

Hi,

There can be two three ways..

1) choices-

When the distance covered is same at two different speeds A and B, the average speed is\(\frac{2AB}{A+B}\)...

here let the second speed be x so average =\(\frac{2*x*65}{x+65}= 50\)................\(130x= 50x + 50*65............80x = 50*65 \approx{50*64}...............x = 40\)....

so, if the distance travelled was same, speed would be nearly 40....

But here distance travelled at 65 is 65% of total distance, so speed for lesser distance has to be less than 40..

ONLY 35 is in choice

E

2) let the distance be 100 miles..

65% = 65 miles...

so time taken to travel \(65 miles @ 65mph = \frac{65}{65}= 1\)hr....

Total time takem = \(100 miles @ 50mph = \frac{100}{50} =2\)hr...

so the remaining 35% or 35 miles was travelled in 1 hour, so speed = 35/1 = 35mph

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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