A bit of maths...

To the kid who got stumped at 12 x 13 question this morning (and all other bright ones out there):

For 12 multiplication such as 12 x13:

 Multiply 2 x 3 = 6 . This will be unit digit.
 Next add 2 and 3  = 5. This will be tens digit.
 Next multiply 1 x 1 = 1. This will be hunderth digit.

So the answer will be 156.


It becomes slightly more complication when we reach 15 and greater numbers, i.e., 12 x 15. Again:

 Multiply 2 x 5 = 10. So '0' will be unit digit and '1' will be carried over to tens place.
 Add 2 and 5  =7. Now add carried over 1 in this total. So we essentially add 2, 5, and 1 (which was carried over in last step) = 8. This will be tens digit.
 Next multiply 1 x 1 = 1. This will be hundreth digit.

So the answer will be 180 and so on.
(BTW, I like to think of multiplication of 15 by an even number like 12 as multiplication of 30 instead so 15 x 12 = 15 x 2 x 6 = 30 x 6 = 180. Much easier to deal with! :) )

We again run into trouble at 17, ie, 12 x 17:

 Multiply 2 x 7 = 14. So 4 will be unit digit and 1 will be carried over.
 Add 2, 7 and 1 = 10. So 0 will be hundreth digit while 1 will be carried over to next step.
 Multiply 1 x1 and add 1 carried over from last step = 2. This will be hundreth digit.

So the answer will be 204.

Or, you can learn the 12 multiplication table.

P.S.: Fairly sure there must be something about this in vedic maths or some other algorithm. I just figured this one out on the ride home. I was utterly bored. So thanks for giving me something to think about.