BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

rate and average questions

Expert replies
by lalabee » Wed Jan 30, 2008 11:16 pm
Question: G can copy 50 pages in 8 hrs, and S copy 50 pages in 6 hours. to copy 100 page together, they will use how many hours?

===>> (50/8+50/6)*time=100

Question: G drives 50 miles in 8 hrs, and S drives 50 miles in 6 hrs. To drive 100 miles together, they will use how many hours?

It seems like we can combine rates, but we cant do the same thing for average speed? Can anyone explain to me why?


Thanks a lot.
Join the discussion
Source: — Problem Solving |

by simplyjat » Thu Jan 31, 2008 7:10 am
lalabee wrote:To drive 100 miles together
What do you mean by driving together?. In English it means each one drives 100 miles....
simplyjat
Join the discussion

Re: rate and average questions

by Stuart@KaplanGMAT » Thu Jan 31, 2008 7:23 am
lalabee wrote:Question: G can copy 50 pages in 8 hrs, and S copy 50 pages in 6 hours. to copy 100 page together, they will use how many hours?

===>> (50/8+50/6)*time=100

Question: G drives 50 miles in 8 hrs, and S drives 50 miles in 6 hrs. To drive 100 miles together, they will use how many hours?

It seems like we can combine rates, but we cant do the same thing for average speed? Can anyone explain to me why?


Thanks a lot.
How is the second question about average speed?

The question itself is a bit amibiguous, but assuming that you mean "how long will it take them to drive a total of 100 miles", you'd solve it the exact same way as you did the first example.

50m/8h = 25/4 mph

50m/6h = 25/3 mph

combined rate = 25/4 + 25/3 = 6.25 + 8.33 = approx 14.6mph total

100/14.6 = some ugly number under 7, but that's the answer.

Average speed questions are different that total speed questions.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Join the discussion