Question 119289
a cold water faucet could fill a sink in 15 minutes, and a hot water faucet can fill it in 12 minutes. the drain can empty the sink in 25 minutes. if both faucets are on and the drain is open, how long will it take to fill the sink?
:
Let t = time to fill the sink, when all 3 valves are open
Let the full sink = 1
:
{{{t/15}}} + {{{t/12}}} - {{{t/25}}} = 1
:
Find a common multiple of all three denominators, 15*12*25 = 4500, will do it
Multiply equation by 4500
4500*{{{t/15}}} + 4500*{{{t/12}}} - 4500*{{{t/25}}} = 4500(1)
Cancel the denominators and you have:
300t + 375t - 180t = 4500
:
495t = 4500
:
t = {{{4500/495}}}
:
t = 9.1 min or 9 min, 6 sec
:
:
Check solution in original equation
{{{9.1/15}}} + {{{9.1/12}}} - {{{9.1/25}}} = 1
:
.6067 + .7583 - .364 = 1; confirms our solution of 9.1 min
:
Did this make sense to you? Any questions?