How wide is the river?

[Alan Anderson]

Originally Posted by gwross

You have to be careful that you're not dividing by zero, though. (Which would happen in the above example if w = -b or if 2w = b.)

Good point. However, since the above example had (w+b) / u = (2w-b) / v, dividing by zero would require both w = -b and 2w = b. That's only possible if w and b are both equal to zero.

Since the original problem had nonzero values for both a and b, we know that we're not dividing by zero.