Time of completion (Times Tables)

[mgb_phys]

Have you taught him methods like when multiplying by 5 you can just half and multiply by 10, etc?

I still remember in junior school (age 7-8?) standing up and explaining to the teacher that we didn't need to learn all these times-tables because as long as you knew what 2x, 5x and 10x was then it was easy to work out all the others.

(Yes I was that kind of child - I think they breathed a sigh of relief when I left.)

 

[rootX]

I still remember in junior school (age 7-8?) standing up and explaining to the teacher that we didn't need to learn all these times-tables because as long as you knew what 2x, 5x and 10x was then it was easy to work out all the others.

Like
3x6 = (1+2)x(1+5)?

Then, you don't even need to know any table
3x6 = (1+1+1)x(1+1+1+1+1+1)

 

[Chi Meson]

Then there are clever paper calculator tricks, like this
http://www.youtube.com/watch?v=8Mcl3empKkY&feature=related
and this
http://www.youtube.com/watch?v=zK_HmQcuSp0&feature=related

 

[Jimmy Snyder]

That's the basic stuff. I'm still fascinated by multiples of 9. Take any multiple of nine, and add the digits. THey add up to nine. If the sum is more than 1 digit, then add the digits of the sum, and that adds up to nine.

The same procedure works for 3. The proofs are rather satisfying and simple to do.

 

[Chi Meson]

Proofs? Oh, no. That's magic, that is.