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A cyclist rode up and down a mountain along the same route each way. [#permalink]
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A cyclist rode up and down a mountain along the same route each way. What was his average speed for the full trip?

(1) His uphill speed averaged 22 kilometers per hour, and his downhill speed averaged 48 kilometers per hour.

(2) The route is 16 kilometers each way.
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Re: A cyclist rode up and down a mountain along the same route each way. [#permalink]
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marcuccio wrote:
A cyclist rode up and down a mountain along the same route each way. What was his average speed for the full trip?

(1) His uphill speed averaged 22 kilometers per hour, and his downhill speed averaged 48 kilometers per hour.

(2) The route is 16 kilometers each way.


Please search before posting. Thank you.
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Re: A cyclist rode up and down a mountain along the same route each way. W [#permalink]
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You can directly use the forumla - 2ab/(a+b) where a and b are the speeds and the distance is the same.

therefore, 1st statement is sufficient.

ans. A
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A cyclist rode up and down a mountain along the same route each way. W [#permalink]
but how do we know the exact degree of the angle of the uphill drive and downhill drive of the mountain? , what if the degree of angle was different for the uphill and downhill, for us to assume that both distances were equal wouldn't we also have to assume that the degree of angle was same for both, an assumption that goes beyond the understanding for a DS question in the GMAT. I hence clicked E. but the OA says A, am i missing something? can experts weigh in on this. Bunuel?
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Re: A cyclist rode up and down a mountain along the same route each way. [#permalink]
marcuccio wrote:
A cyclist rode up and down a mountain along the same route each way. What was his average speed for the full trip?

(1) His uphill speed averaged 22 kilometers per hour, and his downhill speed averaged 48 kilometers per hour.

(2) The route is 16 kilometers each way.



We can calculate Average speed by knowing the rate for up and down trip .
Statement 1 is sufficient .

22 Kms/ Hr --- 24 hrs -- 528 Kms
48 Kms / Hrs --- 11 hrs --- 528 kms

Total average is 1056 / 25 = 30.18 Kms/ hr

Answer is A .
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A cyclist rode up and down a mountain along the same route each way. W [#permalink]
We also can solve though not necessary here but good skills for other questions.

Quick trick to do 96 X 11 quickly or any number X 11. For instance 23 X 11 we do 2___3 and the middle number is adding 2+3 so 253

Or 43X11 is 4__3 and 4+3=7 so the answer is 473

Now 96 X 11 is 9___6 and 6+9=15 so the middle number is a 5 and we add the 1 to the 9 so 1056

97 X 11 is 9___7 and 9+7 =16 so the middle number is a 6 and add 1 to 9 so it is 1067.

A pretty cool math trick to help in computational speed
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Re: A cyclist rode up and down a mountain along the same route each way. W [#permalink]
We know the distance up and down the mountain is equal; thus, we can say the total distance is 2D.

average speed = 2D / t1 + t2

(1) Gives us the rate. From the rate we can determine the time it took to go up the mountain and the time it took to go down the mountain.

average speed = 1056 / 35 = 30.1 km/hr

(2) Not sufficient. Not able to determine the average speed with only the distance.
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Re: A cyclist rode up and down a mountain along the same route each way. W [#permalink]
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Re: A cyclist rode up and down a mountain along the same route each way. W [#permalink]
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