SOLUTION: A passenger plane and a jet leave at the same time from the same airport, traveling in opposite directions. The jet travels at twice the speed of the passenger plane. They are 2400

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Question 209784: A passenger plane and a jet leave at the same time from the same airport, traveling in opposite directions. The jet travels at twice the speed of the passenger plane. They are 2400 miles apart in 4 hours. Find the speed of the passenger plane and jet.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
write 2 equations, 1 for the passenger plane
and 1 for the jet
d%5Bp%5D+=+r%5Bp%5D%2At%5Bp%5D
and
d%5Bj%5D+=+r%5Bj%5D%2At%5Bj%5D
given:
r%5Bj%5D+=+2r%5Bp%5D mi/hr
d%5Bj%5D+%2B+d%5Bp%5D+=+2400 mi
t%5Bj%5D+=+4 hrs
t%5Bp%5D+=+4 hrs
---------------------------
Now I can rewrite the equations:
d%5Bp%5D+=+r%5Bp%5D%2At%5Bp%5D
d%5Bp%5D+=+r%5Bp%5D%2A4
and
d%5Bj%5D+=+r%5Bj%5D%2At%5Bj%5D
2400+-+d%5Bp%5D+=+2%2Ar%5Bp%5D%2A4
-d%5Bp%5D+=+8r%5Bp%5D+-+2400
d%5Bp%5D+=+2400+-+8r%5Bp%5D
By substitution:
4r%5Bp%5D+=+2400+-+8r%5Bp%5D
12r%5Bp%5D+=+2400
r%5Bp%5D+=+200 mi/hr
and
r%5Bj%5D+=+2r%5Bp%5D
r%5Bj%5D+=+2%2A200
r%5Bj%5D+=+400 mi/hr
The speed of the passenger plane is 200 mi/hr
The speed of the jet is 400 mi/hr
check:
d%5Bp%5D+=+r%5Bp%5D%2At%5Bp%5D
d%5Bp%5D+=+200%2A4
d%5Bp%5D+=+800
and
d%5Bj%5D+=+r%5Bj%5D%2At%5Bj%5D
d%5Bj%5D+=+400%2A4
d%5Bj%5D+=+1600
d%5Bp%5D+%2B+d%5Bj%5D+=+800+%2B+1600
d%5Bp%5D+%2B+d%5Bj%5D+=+2400 mi
OK