Question 1207781
<pre>
A bathroom tub will fill in 15 minutes with both faucets open and the stopper in place. With both faucets closed and the stopper removed, the tub will empty in 20 minutes. How long will it take for the tub to fill if both faucets are open and the stopper is removed?


My equation is this:

(x/15) + (x/20) = 1

You say?


NOPE.....WRONG!!
Let T be the time it takes to fill the tub, when both faucets are turned on and the stopper is removed
The 2 faucets, when turned on, can FILL the tub in 15 minutes, or FILL {{{(1/15)^th}}} of tub in 1 minute
Also, the stopper, when removed, can cause the tub to EMPTY in 20 minutes, or cause {{{(1/20)^th}}} of tub to EMPTY in 1 min
We then get the following COMPLETE-JOB equation: {{{matrix(3,3, T(1/15 - 1/20),"=", 1, T((4 - 3)/60), "=", 1, T(1/60), "=", 1)}}} 
<font size = 4><font color = red><b>Time it takes to fill the tub, when both faucets are turned on and the stopper is removed</font></font></b>, 
                                                       or T = 1 <font size = 4><font color = blue><b>÷</font></font></b> {{{1/60}}} = 1(60) = <font size = 4><font color = red><b>60 minutes</font></font></b></pre>