Three pipes A, B and C can fill a tank separately in 8

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Three pipes A, B and C can fill a tank separately in 8 h,10 h and 20h, respectively. Find the time taken by all the three pipes to fill the tank when these pipes are opened together ?

1. 5⁷/₁₁ h
2. 4⁷/₁₁ h
3. 8⁷/₁₁ h
4. 3⁷/₁₁ h

Correct Option: D

Part filled by A in 1 h = 1/8
Part filled by B in 1 h = 1/10
Part filled by C in 1 h = 1/20
Part filled by (A + B + C) in 1 h = 1/8 + 1/10 + 1/20
= (5 + 4 + 2)/40 = 11/40
∴ Required time to fill the tank = 40/11 h
= 3⁷/₁₁ h