Gifted Issues Discussion homepage Forums Learning Environments What is 15 minus 9?

Here is the funny thing. DC6 and 11 months can do 30-20, 120-10 or 150-5 as DC appears to understand the concept. DC also understands her 2x and 3x and 5x and 10x. DC can do 3x4 and 5x6 etc. DC gets it.

But if we ask her verbally or on paper what is 15-9 or 14-8 or 17-9, then there is the longest pause ever.

So just tonight we did 15 minus 9. I asked what DC was thinking. DC said is there a 5 in 9? Yes. DC says 15 take away 5 is 10. Then what is left is 4, so 10 take away 4 is ... long pause, 6.

Oh boy. Talk about over thinking it. Can you guys tell me what is going on and what I can do to help DC with all the "easy" questions? (DC has told me DC is not feeling challenged in math and taking a long time to finish it in class, so teacher thinks DC just needs a lot of time to think.)

thanks!

The way to improve the speed of basic math caculating, probably you have to remember the addtion and substraction tables

My son only remember addtion table and times table, substraction and division just oppsite.

I think there is not much tricks to improve it, she surely understand what minus mean, she just need remember the fact and practice over and over again, even it is bit boring.


Although my son get very good memory of numbers, after a while he still forget and have to pick it up again.

Hmmmm... In maths club, I find that subtraction and addition are normally MUCH slower than multiplication and division. Students can't rely on their working memory to just spurt out the answer and many tire from having to work! I'm coming to the conclusion that many students (regardless of their IQ) don't appreciate the real value in learning number partners - to 10, 20, 50 and 100. Once you really know these number partners and use them to scaffold your learning, seemingly complicated algorithms become much easier. Try drilling number partners in the car (you say 6; s/he says 4, you say 17; s/he says 3, etc.) And then also introduce strategies such as 25+9 = 25+10-1... This can also be extended to 25+8 = 25+10-2... I think it comes back to being really really really familiar with the number system and using 10s, 20s, 50s and 100s as major building blocks.

Anyway, just some thoughts... jojo