Multiplying two numbers

Question

I've come across this technique to multiply two numbers of multiple digits and its not long multiplication. I'd appreciate it if someone could throw some light on why it works or the logic behind it.

1 2 3
x 4 5 6
-------
1 x 456 =  4  5 6
2 x 456 =     8 10 12
3 x 456 =       12 15 18
----------------------------
 sum    =  4 13 28 27 18
----------------------------
fix carry =  5  6  0  8  8

score 2 · Accepted Answer · answered Feb 11 '14 at 05:07

2

This is long multiplication. You've just saved up all the carries to do all at once at the end. You are doing exactly the same multiplications, carries, and additions you would do in long multiplication.

But it does shed some light on why long multiplication works, doesn't it?

answered Feb 11 '14 at 05:07

MPW

43,638

interesting, I dint know you could delay carry like that – Aks Feb 11 '14 at 05:13
I believe this is either the technique or closely related to the traditional technique the Chinese developed for multiplication. (Works just fine...) – colormegone Feb 11 '14 at 06:28

score 2 · Answer 2 · answered Feb 11 '14 at 05:07

2

It's exactly long multiplication with carries delayed.

answered Feb 11 '14 at 05:07

Robert Israel

448,999

Multiplying two numbers

2 Answers2