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Jenny takes 3 hours to sand a picnic table; Laila can do the

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GMAT Club Legend
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Joined: 07 Jun 2014
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Jenny takes 3 hours to sand a picnic table; Laila can do the [#permalink] New post 18 Jun 2018, 15:02
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Question Stats:

90% (01:03) correct 10% (00:00) wrong based on 10 sessions
Jenny takes 3 hours to sand a picnic table; Laila can do the same job in \(\frac{1}{2}\) hour. Working together at their respective constant rates, Jenny and Laila can sand a picnic table in how many hours?

(A) \(\frac{1}{6}\)
(B) \(\frac{2}{9}\)
(C) \(\frac{1}{3}\)
(D) \(\frac{3}{7}\)
(E) \(\frac{5}{6}\)
[Reveal] Spoiler: OA

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Re: Jenny takes 3 hours to sand a picnic table; Laila can do the [#permalink] New post 19 Jun 2018, 06:03
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sandy wrote:
Jenny takes 3 hours to sand a picnic table; Laila can do the same job in \(\frac{1}{2}\) hour. Working together at their respective constant rates, Jenny and Laila can sand a picnic table in how many hours?

(A) \(\frac{1}{6}\)
(B) \(\frac{2}{9}\)
(C) \(\frac{1}{3}\)
(D) \(\frac{3}{7}\)
(E) \(\frac{5}{6}\)


Part of 1 hour work by Jenny = 1/3

Part of 1 hour work by Laila = 1 / 1/2 = 2.

Now part of 1 hour work by both = 1/3 + 2 = 7/3.

Now time inversely prop to work =? 3/7.
GMAT Club Legend
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Joined: 07 Jun 2014
Posts: 4722
GRE 1: Q167 V156
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Re: Jenny takes 3 hours to sand a picnic table; Laila can do the [#permalink] New post 10 Jul 2018, 05:41
Expert's post
Explanation

Since the two women are working together, add their rates. To find their individual rates, divide work by time. Never divide time by work! (Also, be careful when dividing the work by \(\frac{1}{2}\).

The rate is the reciprocal of \(\frac{1}{2}\), or 2 tables per hour.)

Find Jenny and Laila’s combined rate, then divide the work required (1 table) by this rate: 1 table ÷ \(\frac{7}{3}\) table per hour = \(\frac{3}{7}\) hour.

Attachment:
image1.jpg
image1.jpg [ 60.76 KiB | Viewed 196 times ]



Hence option D is correct!
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Re: Jenny takes 3 hours to sand a picnic table; Laila can do the   [#permalink] 10 Jul 2018, 05:41
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Jenny takes 3 hours to sand a picnic table; Laila can do the

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