Calculating 25 minutes by burning 2 inconsistently burning 1-hour ropes

You are given two ropes and are told that they burn at inconsistent rates, but will always take 1 hour to completely burn up. This means that cutting one of the ropes perfectly in half will not give you two smaller 30-minute ropes.

You are told that you need to approximately calculate 25 minutes by burning these ropes in some fashion.

How do you accomplish this?

Hint:

first ½ of hint

I carefully chose approximately instead of precisely

second ½ of hint

because to calculate it precisely would require that you ignite an infinite number of flames