Question 1203160
How do I go about setting up this equation?

2 trains are a mile and a 1/2 apart

A is traveling at 3/4ths the speed of train B

they'll collide in 4 1/2 minutes

how fast is each train going
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The fact that they'll collide implies they're moving toward each other, so the speeds are added.
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A = 0.75B
A + B = 1.75B (the "closing speed")
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d = r*t
1.5 = 1.75B*4.5
B = 1.5/(1.75*4.5) = 1/5.25 miles/minute
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A = 0.75B = 1/7 miles/minute
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Multiply by 60 to get miles per hour