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Kerri drives $150$ miles to visit her grandmother. She starts off driving $60$ miles per hour, but then encounters road construction and has to drive $20$ miles per hour the rest of the way. If she spends the same amount of time at the faster speed as at the slower speed, then how many hours did her $150$-mile trip take in total?

 Jan 13, 2020
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Call the time at both speeds, T

 

And  rate x time  =  distance

 

So

 

60T  + 20T   = 150

 

(60 + 20)T = 150

 

(80)T =  150      divide both sides by  80

 

T  = 15/8   hrs  at both speeds

 

So...the total trip  takes  2T  =  2*  (15/8) =   30/8  =  15/4 hrs   =  3.75 hrs in total

 

 

cool cool cool

 Jan 13, 2020

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