Question 150241
The answer is right, 160 minutes.
We'll look how it arrived there. Rememeber the following,
Rate of {{{A=15L/hr}}}
Rate of {{{B=10L/hr}}}
Pipe {{{A}}}={{{50L/(15L/hr)}}}=3.333hrs=200 minutes it takes to fill the tank
Pipe {{{B}}}={{{50L/(10L/hr)}}}=5 hours= 300 minutes it takes to fill the tank
.
It took {{{100 minutes}}} for Pipe A alone to fill the tank at first. You see above, it needs 200 minutes for A to fill 50L tank. By ratio & proportion,
{{{50L/200minutes=x/100minutes}}}
x=25L (remaining volume to fill)
It just makes sense, only half of the total time he used (100 min), so only half of the tank remains (25L).
Now, to continue filling the remaining 25L, Pipe B joins the process.
We need to add the rate of Pipe A + Rate of Pipe B for the remining task:
{{{(15L/hr)+(10L/hr)=25L/hr}}}
Then,
{{{x=25L/combined rate=25L/(25L/hr)}}}= 1 hour = 60 minutes
.
In conclusion, we add this 60 minutes (Both A & B) + 100 minutes (alone Pipe A)= 160 minutes
Thank you,
Jojo