BTGmoderatorDC wrote:Jane walked for 4 miles. What was her average speed for the first 2 miles?
(1) Jane's average speed for the 4 miles was 3.2 miles per hour.
(2) It took Jane 15 minutes longer to walk the second 2 miles than it took her to walk the first 2 miles.
OA C
Source: GMAT Prep
Say Jane's average speed for the first 2 miles is x mph and average speed for the last 2 miles is y mph.
We have to get the value of x.
Let's take each statement one by one.
(1) Jane's average speed for the 4 miles was 3.2 miles per hour.
2/x + 2/y = 4/3.2 => 1/x + 1/y = 1/1.6 => y = 1.6x/(x - 1.6)
Insufficient since we do not have the value of y to get x.
(2) It took Jane 15 minutes longer to walk the second 2 miles than it took her to walk the first 2 miles.
=> 2/x = 2/y - 15/60
2(1/x - 1/y) = -1/4
1/y - 1/x = 1/8 => y = 8x/(x + 8)
Insufficient since we do not have the value of y to get x.
(1) and (2) together
From y = 1.6x/(x - 1.6) and y = 8x/(x + 8), we have 1.6x/(x - 1.6) = 8x/(x + 8) => x = 4 mph. Sufficient
The correct answer:
C
Hope this helps!
-Jay
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