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I drove to the beach at a rate of 40 miles per hour. If I had driven at a rate of 30 miles per hour instead, then I would have arrived 20 minutes later. How many miles did I drive?

 May 20, 2020
 #5
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Guest, it's obviously not 70. Use your brain. And if you math teacher says 70 is the answer then he/she's obviously incompetent.

 

Let's say x is the time in hours.

 

Since it would take 20 more minutes, so we have 20/60 = 1/3.

 

TRIP____________speed______time___________distance
Actual___________40________x______________40x
Hypothetical_____30_______x+30/40_________30(x+1/3)

 

So the distances are equal so

40x = 30(x+ 1/3) 

40x = 30x + 10

10x = 10

 

x = 1

 

Now let's plug x in. x * 40 = 40 so 40 miles.

 

Checking...

 

40 mph for 40 miles means 1 hour, 30 mph for 40 miles means 1 1/3 hour, and 1 hour is 60 minutes, 1 1/3 hour is 80, 80-60 = 20.

 

Boom.

 

Guest, use your brain.

 

If you don't understand anything feel free to ask.

 May 20, 2020

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