DO NOW:  You go to Red Lobster's to eat and spend $125 and the waitress was great and you want to leave her a nice tip.  The general tip is 15% you want to leave a 20% tip ?

You first put 20% into a faction which is 20 over 100 but to make it easier you simplify it to 1 over 5. You also simplify 125 over 1 to 25 over 1. Then you multiply the fractions which equals 25.