A tank is connected with four pipes A, B, C and D of which two are filling the tank and other two are emptying it. The time taken by A, B, C and D to finish their jobs is 10hours, 15 hours, 20 hours and 30 hours respectively. All four pipes are opened. When the tank was empty, it took 12 hours to fill it completely. Which two are the outlets of the pipes?
1
A and C
2
A and B
3
C and D
4
B and D
5
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