The people in the video (the parents and the chef) have multiple problems with their math. In their division, they skipped the 2 in both videos and moved on to the second number as an individual. They should have gone on to add the second number on the end to make a 2 digit number then divide from that. In multiplication, both people did the first step right. Then the chef forgot, when he multiplied the 7 by the 1, that the 1 was actually a 10, so he got 7 instead of 70.  In the other video, the mom made the same mistake with the 1 and the 5. In addition, both counted the 1’s column correctly but again, the 10’s column was counted as 1’s instead. This can work for any one digit number and two digit number that the first digit in the two digit number is smaller than the one digit number. Also, the second digit of the two digit number has to be smaller than the one digit number. The two digit number also has to be divisible by the one digit number for it to be a trick. For example, 48÷6 could work