Question

Find the time at which the depth of the water in the tank is eual to half its initial depth. D(t)=sqrt(100-2t)
the tank is empty when t=50 min

Answer 1

at t=0, D is sqrt100=10
so what time is D=5
5=sqrt(100-2t)
solve that for t.

Answer 2

So what is the depth when full, when t=0?

We want to make sqrt(100-2t) = half of that, which is 5.

sqrt(100-2t) = 5

Square both sides.

Subtract 25 from both sides.

Now t is easy.