Answer:
time require is 23.33 hours
Explanation:
given data
time t1 = 7 hours
time t2 = 10 hours
to find out
how long it take to fill vat if both pipe left open
solution
we consider here vat volume is v
so speed = volume / time   .................1
inlet speed  = v / 7         .................2
outlet speed = Â v / 10 Â Â Â Â Â Â ..................3
so from equation 2 and 3
net speed is = v / 7 Â - Â v / 10
net speed = 3 /70 × v
so here time is
time = v  / net speed
time = [tex]\frac{v}{\frac{3v}{70} }[/tex]
time = 70 / 3 = 23.33
so time require is 23.33 hours