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If it takes Daniel 9 hours to clean an office building and it takes Ma

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If it takes Daniel 9 hours to clean an office building and it takes Ma  [#permalink]

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New post 22 Nov 2018, 00:12
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

88% (01:02) correct 12% (01:01) wrong based on 25 sessions

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If it takes Daniel 9 hours to clean an office building and it takes Mark 6 hours, how long would it take the two of them, working together, to clean the building?

A. 3 hours
B. 3 hours 36 minutes
C. 4 hours 45 minutes
D. 6 hours
E. 7 hours 30 minutes

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If it takes Daniel 9 hours to clean an office building and it takes Ma  [#permalink]

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New post 22 Nov 2018, 00:36
Work done by Daniel in 1 hour = \(\frac{1}{9}\)

Work done by Mark in 1 hour = \(\frac{1}{6}\)

Together work done = \(\frac{1}{9}\) + \(\frac{1}{6}\)

= \(\frac{5}{18}\)

This is work done in 1 hour. So they can complete the work in \(\frac{18}{5}\) hours or 216 minutes or 3 hours 36 minutes.

OPTION: B
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Re: If it takes Daniel 9 hours to clean an office building and it takes Ma  [#permalink]

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New post 22 Nov 2018, 00:47
Bunuel wrote:
If it takes Daniel 9 hours to clean an office building and it takes Mark 6 hours, how long would it take the two of them, working together, to clean the building?

A. 3 hours
B. 3 hours 36 minutes
C. 4 hours 45 minutes
D. 6 hours
E. 7 hours 30 minutes


combined hours :1/9+1/6
= 54/15
or 54*60/15= 216 minutes or 180 + 36 mins or 3 hrs and 36 mins option B
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Re: If it takes Daniel 9 hours to clean an office building and it takes Ma  [#permalink]

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New post 23 Nov 2018, 03:44
Bunuel wrote:
If it takes Daniel 9 hours to clean an office building and it takes Mark 6 hours, how long would it take the two of them, working together, to clean the building?

A. 3 hours
B. 3 hours 36 minutes
C. 4 hours 45 minutes
D. 6 hours
E. 7 hours 30 minutes



Total time = (A)(B)/(A+B)......where A & B are times.


Total time = 54/15 =3.something........only one answer fits

Answer: B
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Re: If it takes Daniel 9 hours to clean an office building and it takes Ma &nbs [#permalink] 23 Nov 2018, 03:44
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