11 times table trick | multiply by 11 | multiplication tricks #multiply #multiplication #shorts

[nezgyulnez]

You can actually see how this works using Algebra: A 2-digit numbercan be represented by the expression 10a+b if we then multiply this number by 11 we get 11(10a+b)=110a+11b we can then dolit the coefficients of a and b into sums of powers of 10, so 110a+11b=100a+10a+10b+b if we then factor, we get 100a+10(a+b)+b Therefore, thr 100s-digit is simply the same as the original 10s The unit remains the same, and the 10s digit is the sum of both digits What about if we have a 3 digit number, i.e. 100a+10b+c If we multiply this by 11we get 1110a+110b+11c Again, if we split the coefficients into the sum of 10s we get: 1000a+100a+100b+10c+c If we then factor put the common coefficients, we get: 1000a+(100a+b)+10b+c)+c

Therefore, we can do plan B, lets say we have 11×79 put 7 in the 9 plus it put it in the middle so 7+9=16 Therefore, we cant put it so we add 1 to the 7 so it becomes 8 So the answer is 869.