1 POOL, the unit of volume
Oultet at the rate 1/x
Inlet at the rate 1/y
t, time used in filling 1 pool in the step-wise process described
Filling and Emptying in 8 hours
rate time quantity
FILL 1/y t (1/y)t
EMPTY 1/x 8-t (1/x)(8-t)
Total 8 1
This gives an equation .
The fill process with BOTH pipes open gives and the best you might do is to solve for and substitute into the step-wise equation; but you will still have the UNKNOWN variables of t and y.
Your problem description seem incomplete. No finished answer. Maybe another tutor will see a better way.
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, LCD 7.5y;
----------still the two unknowns y and t.