Thread: Find Average Rate of Speed

Originally Posted by magentarita

Maryann drove 280 miles to attend a marine biologist conference and arrived 1 hour late. Maryann figured out that, had she increased her average speed by 5 mph, she would have arrived on time. What was her average rate of speed?

Isn't the average rate found using r = D/t?

Yes, that is the equation to use. How far have you gotten in applying it?

. . .actual:
. . . . .distance: 280
. . . . .rate: r
. . . . .time: 280/r

. . .possible:
. . . . .distance: 280
. . . . .rate: r + 5
. . . . .time: ..?..

Complete the table. Then note the relation: "(possible time) is (actual time) less (one hour)". Translate this into an equation, and solve the rational equation for the value of "r".

If you get stuck, please reply with a clear listing of your steps and reasoning so far. Thank you!

Originally Posted by stapel

Yes, that is the equation to use. How far have you gotten in applying it?

. . .actual:
. . . . .distance: 280
. . . . .rate: r
. . . . .time: 280/r

. . .possible:
. . . . .distance: 280
. . . . .rate: r + 5
. . . . .time: ..?..

Complete the table. Then note the relation: "(possible time) is (actual time) less (one hour)". Translate this into an equation, and solve the rational equation for the value of "r".

If you get stuck, please reply with a clear listing of your steps and reasoning so far. Thank you!

possible time = D/r, which is the same as 280/(r + 5) = t



The equation becomes: 280/(r + 5) = 280/r - 1

I pretty much can do the rest. I have trouble, like most people, setting up the right equation from the information given in certain word problems. This is a common problem with students. Do you have questions involving average rate of speed in your purplemath website?