How do I multiply a triple digit number by a double digit?
142 x 12 = ?
I’m sure that you’ll agree that there are many methods that we can use.
Which method do you feel most comfortable with?
Try your method to solve one of the problems on this page. When you
are finished, explain your method to your partner.
156 x 14 = ?
Here’s a new method for you to try!
My problem is: 145 x 13 = ?
Step one:
Break the numbers up into their different parts.
145 = 100 + 40 + 5
13 = 10 + 3
Step two:
Fill the numbers onto a grid like this.
x
10
3
100
40
5
Step 3:
Begin to cross multiply each number filling the answer into the grid.
(This is just like filling in a multiplication square.)
x
100
40
5
10
1000
400
50
3
300
120
15
Step 4:
Add up each row of numbers and put your total at the side of the
column.
x
3
100
40
5
1000
400
50
1450
300
120
15
435
Step 5:
Simply add the two numbers together to get your final
answer.
1450
+ 435
How easy is that?
1885
Therefore:
145 x 13 = 1885
Challenge!
Can you use this new method to
solve the problem below?
134 x 15 = ?
We can use this grid to solve problems
together.