It’s all a matter of breaking a number down into its components.
The number 123 means 100+20+3.
Suppose we want to multiply this number by 456 which breaks down into 400+50+6.
Write: 100+20+3 times 400+50+6.
We take each component from the left and multiply each of the components on the right.
100×400=40000
100×50= 5000
100×6= 600 Add these up 45600
Now 20 from the left:
20×400=8000
20×50= 1000
20×6= 120 Add these up 9120
Finally
3×400=1200
3×50= 150
3×6= 18 Add these up 1368
Now we add all the partials together:
45600
9120
1368
———
56088