really easy on paper, in your head, not so easy. In your head, here's how I'd do it: 13 squared is 169- that's easy. then, 10 times 19 is 1690, and 3 times 169 is approx 500, so 2190 is an easy approximation. Only 7 off from the actual answer!

how long did it take you to answer this? I assume thats what they were testing

2197

Do it on your head. 13*13 = 169. For 169*13 first 3*169 = 507 second 10*169 = 1690 Finally 169*13 = 507 + 1690 = 2197.

I did it while doing some chit chat about his day. No longer then two minutes, and then he asked how I did it. So I explained the steps.