Question 195402
Helped by a strong jet stream, a LA to Boston plane flew 10%faster than usual
 and made the 4400KM trip in 30 min less time than usual.
 At what speed does the plane usually fly?
:
Let s = usual speed of the jet
then
1.1s = the faster speed
:
Change 30 min to hrs; {{{1/2}}} hrs
:
Write a time equation: Time = {{{dist/speed}}}
:
faster time + .5 hr = usual time
{{{4400/(1.1s)}}} + {{{1/2}}} = {{{4400/s}}}
get rid of those annoying denominators, multiply equation by 110s:
110s*{{{4400/(1.1s)}}} + 110s*{{{1/2}}} = 110s*{{{4400/s}}}
cancel out the denominators, results
100(4400) + 55s = 110(4400)
:
440000 + 55s = 484000
:
55s = 484000 - 440000
:
55s = 44000
s = {{{44000/55}}}
s = 800 mph is the usual speed
;
:
Check solution by finding the times:
4400/800 = 5.5 hrs
4400/(1.1*800) = 5 hrs; confirms our solution