Question 208618
The average speed of today's plane is twice that of a plane of 5 years ago and
 takes 1 1/4 hours less time to fly the same distance of 1500 miles.
 find the average speed of a plane of 5 years ago?
:
let s = speed 5 yrs ago
then
2s = speed today
:
Write a time equation: Time = {{{dist/speed}}}

{{{1500/s}}} - {{{1500/(2s)}}} = 1.25
Multiply 2s, results
2(1500) - 1500 = 1.25(2s)
:
3000 - 1500 = 2.5s
:
1500 = 2.5s
:
s = {{{1500/2.5}}}
s = 600 mph speed 5 yrs ago
:
:
Check solution by finding the times
1500/600 = 2.5 hrs
1500/1200 =1.25 hrs
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time diff: 1.25 hrs