We first learned how easy it is to multiply single digits by 11....easy: 2 x 11 is 22. 8 x 11 is 88.
But what do we do when we have 2 digit numbers to multiply by 11? Well, it turns out to be just as easy! 32 x 11 is 352 and 45 x 11 is 495....see a pattern here?
For 32 x 11, put the sum of 3 and 2 (5) between 3 and 2, and for 45 x 11, put the sum of 4 and 5 (9) between 4 and 5. So, let's try a couple:
1. 27 x 11 =
2. 34 x 11 =
3. 51 x 11 =
4. 63 x 11 =
5. 81 x 11 =
get it?
1. 297 the sum of 2 and 7 (9) between 2 and 7
2. 374 the sum of 3 and 4 (7) between 3 and 4
3. 561 the sum of 5 and 1 (6) between 5 and 1
4. 693 the sum of 6 and 3 (9) between 6 and 3
5. 891 the sum of 8 and 1 (9) between 8 and 1
Amaze your friends and family by showing them this trick.
What to do in the case where the 2 digits add up to more than 9? Just carry the 1.
For example: 39 x 11 is (3 + 9 in the middle 12...put down the 2 carry the 1 to the 3) so the answer is 429....easy, right?