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Two bicycle wheels, A and B, start rotating at constant speeds at the

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Two bicycle wheels, A and B, start rotating at constant speeds at the  [#permalink]

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New post Updated on: 18 Jul 2018, 19:16
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Question Stats:

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Two bicycle wheels, A and B, start rotating at constant speeds at the same time., How many seconds after the wheels start rotatins will wheel B have made 6 more rotations than wheel A?

(1) The rate of rotation of wheel B is three times that of wheel A
(2) The two wheels average 40 revolutions per minute

Originally posted by franteraoka on 18 Jul 2018, 13:30.
Last edited by Bunuel on 18 Jul 2018, 19:16, edited 1 time in total.
Edited the question.
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Re: Two bicycle wheels, A and B, start rotating at constant speeds at the  [#permalink]

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New post 18 Jul 2018, 20:11
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franteraoka wrote:
Two bicycle wheels, A and B, start rotating at constant speeds at the same time., How many seconds after the wheels start rotatins will wheel B have made 6 more rotations than wheel A?

(1) The rate of rotation of wheel B is three times that of wheel A
(2) The two wheels average 40 revolutions per minute


(1) Let wheel A rotate 'x' times per unit time, so B rotates '3x' times per unit time. But without knowing 'x', we cannot answer the time it will take for B to make 6 more rotations than A. Not sufficient.

(2) Clearly this statement is not sufficient, as this doesnt tell us anything about rotations of A and B individually nor do we know which wheel makes more rotations.

Combining, let A makes x rotations per minute, and B makes 3x rotations per minute. Then: (x+3x)/2 = 40 or x = 20. So A makes 20 rotations per minute and B makes 60 per minute. In 60 seconds, B makes 40 more rotations than A. So to make 6 more rotations, B needs = 40/60 * 6 = 4 seconds. Sufficient.

Hence C answer
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Re: Two bicycle wheels, A and B, start rotating at constant speeds at the &nbs [#permalink] 18 Jul 2018, 20:11
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Two bicycle wheels, A and B, start rotating at constant speeds at the

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