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
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