SOLUTION: One plane can travel 20 miles per hour faster than another. One of them goes 450 miles in the same time it takes the other to go 420 miles. What are their speeds?

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Question 766094: One plane can travel 20 miles per hour faster than another. One of them goes 450 miles in the same time it takes the other to go 420 miles. What are their speeds?
Answer by josgarithmetic(39629) About Me  (Show Source):
You can put this solution on YOUR website!
The larger distance goes with the faster plane.

Let r = slower plane speed
let x = unknown time for travel

PLANE__________speed__________time_________distance
SLOW___________r______________420/r________420
FAST__________r+20____________450/(r+20)____450

The two time expressions are equal, according to the description.
420%2Fr=450%2F%28r%2B20%29
420%28r%2B20%29=450r
420r%2B8400=450r
8400=30r
r=840%2F3
highlight%28r=380%29 mph.