We can expand on the first tip to learn how to multiply the number eleven faster and more accurately with some more complications. If you have any questions or feedback please feel free to add a comment to the post.
Example: 75 * 11 = 825.
When multiplying a two digit number by 11 there are three steps to follow for the non-eleven multiplier to quickly get the answer.
Step 1) The ones place in the answer is equal to the ones place in the non-eleven multiplier, the far right digit - the number 5 in our example. Our answer now has one digit filled in _ _ 5
Step 2) The next number in the answer is the sum of the two digits in the non-eleven multiplier; 7 and 5 in the example, which is equal to 12. We take the digit in the sum's ones place as the next digit in our answer.
The answer is missing only one more digit _ 25
Since the sum of of 7 and 5 is 12, which has two digits, we carry over the ten's place digit (1) into step 3.
Step 3) The last digit in the answer is the digit in the ten's place in the non-eleven multiplier (7) plus the carry over from Step 2 (1). The last digit in our answer is the sum of 7+1. The answer is 825.
In Step 3 the most we would add to the digit is 1 because the highest carryover is the number 1; no two digit sums are equal to or greater than 20.