3 ms·
Cute but it does kind of predictably fall down when you're doing 9s and 8s instead of 2s and 3s.
by Avshalom 17y ago
Cute but it does kind of predictably fall down when you're doing 9s and 8s instead of 2s and 3s.
- deleted 17y ago[deleted]
- Avshalom 17y agoI meant that when you're doing say 987 * 659 you end with an entire page of lines and having to count up 9 groups of cross each > 40, for instance in the case of the middle column: accurately count and add 81, 40, 42. The method still works fine it just becomes a hassle with a lot of chance for mistake (miscounting mostly) and looks way less elegant. I like it too though, I just wouldn't teach it to a kid and then tell him to do 98*79.
- RiderOfGiraffes 17y agoSorry, I deleted my comment because it took me a moment to realise what you were saying. Yes, you're right. Here's how I avoid the problem. When I've use this method as an adjunct I've put two lines with a circle around them then labelled the "bundle" with how many lines there are. That way I can "have lots of lines" without actually drawing them all. The diagrams look similar, the method clearly works, and when I have used it, it's led the students to try to work out why it works, occasionally with success. I've found it to be a useful extra tool for teaching these things. BTW, I'm not the person in the video, it's just that I know and have used this technique.
- Retric 17y agoI would like to mention to you that this is really just another way to visualize traditional multiplication. 999 x 999 results in adding stacks of 81's but with this method you add vertically then horizontally where the traditional method does horizontal then vertical. aka vertical then horizontal: (81 + 81 * 2 * 10 + 81 * 3 * 100 + 81* 2 *1000 + 81 * 1 *10000) Horizontal then vertical: 999 * 9 + 999 * 90 + 999 * 900 = (81 + 810 + 8100) + (81 + 810 + 8100) *10 + (81 + 810 + 8100) * 100 If you chose diffrent groupings you can merge the two.