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

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Math Expert
Joined: 02 Sep 2009
Posts: 57272
If it takes Daniel 9 hours to clean an office building and it takes Ma  [#permalink]

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22 Nov 2018, 01:12
00:00

Difficulty:

15% (low)

Question Stats:

96% (01:16) correct 4% (01:19) wrong based on 32 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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22 Nov 2018, 01:36
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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22 Nov 2018, 01:47
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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23 Nov 2018, 04:44
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

Re: If it takes Daniel 9 hours to clean an office building and it takes Ma   [#permalink] 23 Nov 2018, 04:44
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