Problem: You have two numbers – X and Y – and you want to figure out what percentage of increase or decrease there is from X to Y.

Solution: I’ve had to do this a bunch of times in my life and while I always come up with the correct answer, it always takes me longer than I think it should.

If X = 2.3125 and Y = 2.3750, you could do this:

(Y – X) / X * 100 = Z

(2.3750 – 2.3125) / 2.3125 * 100 = 2.70270270

That means that if I change the gear ratio on my motorcycle from 2.3125 to 2.3750, that would be a 2.7 percent increase.