Let’s try another one. How about 12 × 17?
The numbers are above 10 so we draw the circles above. How much above 10? Two and 7, so we
write 2 and 7 in the circles.
What do we do now? Because the circles are above, the numbers are plus numbers so we add
crossways. We can either do 12 plus 7 or 17 plus 2. Let’s do 17 plus 2.
17 + 2 =
We now multiply 19 by 10 (our reference number) to get 190 (we just put a 0 after the 19). Our work
now looks like this:
Now we multiply the numbers in the circles.
2 × 7 =
Add 14 to 190 and we have our answer. Fourteen is 10 plus 4. We can add the 10 first (190 + 10 =
200), then the 4, to get 204.
Here is the finished problem:
Test yourself
Now try these problems by yourself.
a) 12 × 15 =
b) 13 × 14 =
c) 12 × 12 =
d) 13 × 13 =
e) 12 × 14 =
f) 12 × 16 =
g) 14 × 14 =
h) 15 × 15 =
i) 12 × 18 =
j) 16 × 14 =
The answers are:
a)
b)
c)
d)
e)
f)
g)
h)
i)