This was an awesome math video, and it’s very humorous too. The guy made you believe that his thinking was true. In his division he uses the two and the eight separately instead of dividing it by twenty-eight itself. He should have done twenty-eight divided by seven. The multiplication, he did three times seven and that equaled twenty-one, then he did seven times one and equaled seven. He added twenty-one and seven that equaled twenty-eight. What he should have done was thirteen times seven and not added, but carries the two from the twenty- one to the seven. That would equal ninety-one. The addition part was a very cool way too. He put down thirteen, seven times. When he added all the threes then he added the ones to it.
If I do his way then I can also do it with fifteen. I figured out that the first digit has to be smaller than the number that’s being divided, and the second number has to be bigger. Fifteen and three work to equal eighteen!