How do you find 81-16 using mental math

Um, all i can say is envision both numbers in your head with 81 directly above 16.

Now, let's start by subtracting 1-6, in this case, you can't put - 5 because these are two digit numbers we are working with and so it wouldn't make sense. Now, we cross out 1 and place it with 11. 11-6=5 so we know the answer ends with 5.

Now let's subtract 8-1. But before we do that, we took one power away from 8 to make 1=11, remember? so now we have 7-1 which equals 6. Put 6 and 5 together and we get 65.

81-16=65