SOLUTION: A tank has two filling pipes attached to it pipe A takes 15 minutes while pipe B takes half an hour to fill the tank if both pipes are opened together after how many minutes must p

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Question 1129314: A tank has two filling pipes attached to it pipe A takes 15 minutes while pipe B takes half an hour to fill the tank if both pipes are opened together after how many minutes must pipe A be turn off so that the time taken to fill the entire tank is 18 minutes?
Found 2 solutions by ikleyn, josgarithmetic:
Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
.
The rate of the pipe A is  a = 1%2F15 of the tank volume per minute.


The rate of the pipe B is  a = 1%2F30 of the tank volume per minute.


The equation is


    a*t + b*18 = 1,    or


    %281%2F15%29%2At + %281%2F30%29%2A18 = 1,


    %281%2F15%29%2At = 1+-+18%2F30 = 1+-+3%2F5 = 2%2F5  ====>


    t = %282%2F5%29%2A15 = 2*3 = 6 minutes.     ANSWER


Answer. Pipe A must be turn off after 6 minutes.

Solved.



Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
x, number of minutes while tank b works alone
18-x, number of minutes A and B both work together

%281%2F15%2B1%2F30%29%2818-x%29%2Bx%2F30=1