We have L= the number of lines of water in the pool t seconds after the pool has been plugged off to drain, = 200(10- t2) Rate at which the water is running out at the end of 5 s = 400(10 - 5) = 2000 L/ s = Final rate Since, initial rate = - (
dL
dt
)t=0 = 4000 L/s ∴ Average of during first 5 seconds =