math?

When watching this video I was very confused. I watched it a second time, but I still felt the same way. Then I ask my parents to watch video as well. My dad understood what was going on, and explained it to me. He started with a number that was a multiple of seven. When you add 7 to the number, the number in the ones column had to be bigger than seven and the number in the tens column has to be smaller than seven. Through trial and error, he came up with 49. Since 7 can’t go into 4, you put that off to the side for later. 7 can go into 9 so 9-7=2. Now you bring back the 4 and that makes 42. 42-42=0. Therefore, 16 X 7=49. To check your work, you can do that by adding 16 (7) times (16+16+16+16+16+16+16=49). 6 X 7= 42 + 7 (1’s)= 49. After trying this process several more times, I also learned that you could use this algorithm with almost any number as long as the rule applies. For example: 3 X 17=24, 6 X 17=49, 7 X 16=49, and 3 X 17=24.

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