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# Driving at a constant speed of 60/mph, Bob can reach his wor

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Senior Manager
Joined: 20 May 2014
Posts: 282
Followers: 15

Kudos [?]: 49 [0], given: 220

Driving at a constant speed of 60/mph, Bob can reach his wor [#permalink]  02 Oct 2017, 22:29
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Question Stats:

66% (01:09) correct 33% (01:32) wrong based on 3 sessions
Driving at a constant speed of 60/mph, Bob can reach his work in 15 min. If he wants to reach work three minutes faster, by how many miles per hour must he increase his speed?

(A) 12 mph

(B) 15 mph

(C) 20 mph

(D) 75 mph

(E) 80 mph

Kudos for correct solution.
[Reveal] Spoiler: OA
Director
Joined: 03 Sep 2017
Posts: 521
Followers: 1

Kudos [?]: 334 [1] , given: 66

Re: Driving at a constant speed of 60/mph, Bob can reach his wor [#permalink]  03 Oct 2017, 04:40
1
KUDOS
Using the usual formula $$speed = \frac{distance}{time}$$, the distance to work is computed as $$60*\frac{1}{4} = 15$$, where 1/4 is 15 minutes in hours.

Then, if we want to reach work in 3 minutes less, it would take 12 minutes or 1/5 hours to get to work. Thus, the speed should be $$15*5 = 75$$. Thus, he needs to go 15 mph faster.

Re: Driving at a constant speed of 60/mph, Bob can reach his wor   [#permalink] 03 Oct 2017, 04:40
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