Question 233179
Joanne left the driveway 40 seconds after Gloria driving down a winding four mile country road. 
If Joanne's speed averaged 25 miles an hour what would Gloria's average speed be for Joanne to catch up to her after the third mile?
:
Let s = Gloria's speed to catch Joanne
;
Let this happen at 3.1 miles
:
Change 40 sec to hrs
{{{40/3600}}} = .011 hrs
:
Write a time equation (Time = {{{dist/speed}}})
;
J.s travel time = G's travel time + 40 sec (.011 hrs)
{{{3.1/25}}} = {{{3.1/s}}} + .011
:
multiply equation by 25s
3.1s = 3.1*25 + .011(25s)
: 
3.1s = 77.5 + .275s
3.1s - .275s = 77.5
2.825s = 77.5
s = {{{77.5/2.825}}}
s = 27.43 mph
:
:
Check by finding the times
3.1/25 = .124 hrs
3.1/27.43 = .113 hrs
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time diff = .011 hrs which is: .011 * 3600 ~ 40 sec