Here is a quick trick to multiply a teen (11-19) by 20. Add 10 to the teen, and then multiply by 10. So if you have 14 times 20, that’s 240. Then multiply the ones part of the teen by 10 and add that, so in this case 4 times 10 is 40 + 240 is 280.

Let’s try a hard one: 17 times 20? That’s 270 + 70 = 340. That’s especially easy because 70 + 70 is 140. How about 18 times 20? Well, that’s 280 + 80. 80 + 80 is 160, add in our 200 and you get 360.

You give it a shot.