Question 812254
You can make your life a lot easier if you learn these three simple formulas
Dist = speed * time
d = s*t
:
Speed = dist/time
s = d/t
;
Time = dist/speed
t = d/s
:
A plane leaves Chicago and flies 750 miles to New York.
 If it takes 2.5 hours to get to New York flying against wind,
 but only 2 hours to fly back to Chicago,
 what is the plane's rate of speed?
: 
let s = speed of the plane in still air
let w = the speed of the wind
then
(s-w) = ground speed against the wind
(s+w) = ground speed with the wind
:
Write a distance equation for each way
2.5(s-w) = 750
 2(s+w)  = 750
Simplify both equation, divide the first by 2.5, the 2nd by 2
s - w = 300
s + w = 375
---------------adding eliminates w, find s
2s = 675
s = 337.5 mph planes speed in still air