Mike has a large tropical fish collection.

Let the number of fish that Mike has be X.

He gives `2/3` of his fish to a local high school. The number of fish remaining with him is `(1 - 2/3)*X = X/3`

Then, he gives `2/5` of the remaining fish to an elementary school. The number remaining with him now is `(X/3)*(1 - 2/5)` = `(X/3)*(3/5) = X/5`

He has 30 fish left finally. `X/5 = 30`

=> X = 150

Mike had 150 fish to start with.