Speed word problem

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joe joe
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Speed word problem

Kevin leaves his bakery at 6:50am to deliver some cookies to a hotel. If he drives at a constant speed of 80km/hr, he will reach time. If he drives at a constant speed of 64km/hr, he will be 10 min late. At waht time is kevin supposed to deliver the cookies to the hotel?

Please help to solve the above problem. Thanks.
Captain Smart Captain Smart
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Re: Speed word problem

distance = rate x time

at 80 km/hr
d = 80t

at 64 km/hr
d = 64(t + 1/6)   time plus 10 minutes or 1/6 of an hour

80t = 64(t + 1/6)   distances are equal
80t = 64t + 32/3   distributed
16t = 32/3   subtracted 64t
t = 2/3   divided by 16
2/3 of an hour is 40 minutes

Add 40 minutes onto 6:50 am

He is supposed to arrive at 7:30 am

~Captain Smart~
joe joe
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Re: Speed word problem

Thanks a lot.