Quick: What is 13 times 11? (In less than a second) "It's 143".

What is 15 times 11? (Again, in less than a second) "It's 165".

You might already see the pattern to how simple this "multiply by 11" trick is, but if not, here's how it works: Start with a number, like 13:

13

Next, take the two numbers, "1" and "3", and move them apart, like this:

1 3

Then in between those two numbers put the sum of those outside numbers. 1 plus 3 is 4, so just put a 4 in there, like this:

143

That's the magic secret to this trick. By the same measure, 15 x 11 is 165. Start with 15:

15

then move the two numbers apart:

1 5

then put the total of 1 + 5 in the middle:

165

Now you too can rapidly multiply two-digit numbers by the number eleven (11).