Thanks - that results in smaller numbers through the steps, which would make it less cumbersome to do in your head. Of course, it would matter less if he could use a calculator.

Interestingly, your approach made me think of another way to use smaller numbers - by keeping 200 squared until the last step:

200^2 - (24/25)(200^2) = w^2

(200^2)/25 = w^2

200/5 = w