When both floodgates A and B are open, a reservoir drains in : PS Archive
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# When both floodgates A and B are open, a reservoir drains in

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VP
Joined: 06 Jun 2004
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When both floodgates A and B are open, a reservoir drains in [#permalink]

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17 Oct 2005, 20:47
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When both floodgates A and B are open, a reservoir drains in 3(1/3) days. If floodgate A alone drains the reservoir in 10 days, how many days does it take floodgate B alone to drain the reservoir?

A. 4
B. 5
C. 6 2/3
D. 10
E. 12

My way of solving follows, let me know if my concept is right.

3 1/3 days = 10/3 days

1/10 + B = 1/ (10/3) => 1/10 + B = 3/10

B = 3/10 - 1/10 = 2/10 = 1/5

GMAT Club Legend
Joined: 07 Jul 2004
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17 Oct 2005, 21:12
A: 10 days -> 1 job; 1 day -> 1/10 job
B: x days -> 1 job; 1 day -> 1/x job

Together: (1/10 + 1/x) job in 1 day = (x + 10)/10x

Together: 10/3 days -> 1 job; 1 day -> 3/10 job = (x+10)/10x

30x = 10x + 100
20x = 100
x = 5 (B)
VP
Joined: 06 Jun 2004
Posts: 1059
Location: CA
Followers: 2

Kudos [?]: 146 [0], given: 0

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17 Oct 2005, 21:26
ywilfred wrote:
A: 10 days -> 1 job; 1 day -> 1/10 job
B: x days -> 1 job; 1 day -> 1/x job

Together: (1/10 + 1/x) job in 1 day = (x + 10)/10x

Together: 10/3 days -> 1 job; 1 day -> 3/10 job = (x+10)/10x

30x = 10x + 100
20x = 100
x = 5 (B)

Thanks, that's what I thought
17 Oct 2005, 21:26
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