SOLUTION: This is totally confusing to me, how do you set this up and solve this problem? Flying agains the jet stream a jet travels 4200 km in 5 hours. flying wih the jetstream, the same

Question 155469: This is totally confusing to me, how do you set this up and solve this problem?
Flying agains the jet stream a jet travels 4200 km in 5 hours. flying wih the jetstream, the same jet travels 10620 km in 9 hours. What is the speed of the jet still in the air, and what is the speed of the jet stream?
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
You must apply the distance formula:
d = rt
where
d is distance
r is rate or speed
t is time
.
Let x = speed of jet stream
and y = speed of the jet in still air
.
Since we have two unknowns, we'll need two equations.
.
From:"Flying against the jet stream a jet travels 4200 km in 5 hours." we get equation 1
5(y-x) = 4200
.
From:"flying with the jet stream, the same jet travels 10620 km in 9 hours." we get equation 2
9(y+x) = 10620
.
Solve equation 1 for y:
5(y-x) = 4200
y-x = 840
y = 840+x
.
Using the above definition of 'y', substitute it into equation 2 and solve for 'x':
9(y+x) = 10620
9(840+x+x) = 10620
9(840+2x) = 10620
840+2x = 1180
2x = 340
x = 170 mph (speed of jet stream)
.
Using the above definition of 'x', substitute it into equation 1 and solve for y:
5(y-x) = 4200
5(y-170) = 4200
y-170 = 840
y = 1010 mph (speed of jet in still air)
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