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Sam can repair a machine in 15 days and Ross can repair in 25 days

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Joined: 03 Feb 2017
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Sam can repair a machine in 15 days and Ross can repair in 25 days  [#permalink]

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New post 24 Jun 2017, 03:02
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Difficulty:

  45% (medium)

Question Stats:

68% (01:52) correct 32% (01:58) wrong based on 71 sessions

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Sam can repair a machine in 15 days and Ross can repair the same machine in 25 days. If they decide to repair the machine on alternate days, with Ross on the first day, followed by Sam on the second day and so on till the repair is completed, how many days do they take to complete the repair work.

A) 17
B) 18
C) 19
D) 20
E) 21
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Re: Sam can repair a machine in 15 days and Ross can repair in 25 days  [#permalink]

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New post 24 Jun 2017, 04:08
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1
Work done by Sam in one day = 1/15, in Ross = 1/25.
Total work done by Sam in the first day and Ross in the second day = 1/15 + 1/25 = 8/75.

No. of days to complete the work: n(8/75) = 1
n = 75/8 = 9.375.

So, it will take 9.375 two day's work, hence 9.375 * 2 = ~19 days.
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Re: Sam can repair a machine in 15 days and Ross can repair in 25 days  [#permalink]

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New post 24 Jun 2017, 06:49
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danlew wrote:
Sam can repair a machine in 15 days and Ross can repair the same machine in 25 days. If they decide to repair the machine on alternate days, with Ross on the first day, followed by Sam on the second day and so on till the repair is completed, how many days do they take to complete the repair work.

A) 17
B) 18
C) 19
D) 20
E) 21


Use LCM:
Portion of the work done by Sam is 1/15 = 5/75;
Portion of the work done by Ross is 1/25 = 3/75.

Together in 2*9 = 18 days they'll do (5 + 3)*9 = 72 parts out of 75. On the 19th day Sam will do the remaining job. So, the answer is 19.

Answer: C.
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Re: Sam can repair a machine in 15 days and Ross can repair in 25 days  [#permalink]

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New post 07 Oct 2018, 20:04
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Re: Sam can repair a machine in 15 days and Ross can repair in 25 days &nbs [#permalink] 07 Oct 2018, 20:04
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