Question 908074
 if you drive a car 135 miles and have a mean of a certain speed.
 if the mean speed had been 4 mph more, you could have traveled 144 miles in the same time.
 what was the mean speed?
:
let s = the mean speed
then
(s+4) = the faster speed
:
Write a time equation, time = dist/speed
actual time = faster speed time
{{{135/s}}} = {{{144/((s+4))}}}
Cross multiply
144s = 135(s+4)
144s = 135s + 540
144s - 135s = 540
s = 540/9
s = 60 mph is the mean speed
:
;
you can confirm this, find the actual time at each speed, should be the same
135/60 = 2.25 hr
144/64 = 2.25 hr