48 Speed Math for Kids
Using 20 as a reference number, we get:
20 18 × 17 =
–2
–3
Subtract diagonally:
17 – 2 = 15
Multiply by 20:
2 × 15 = 30
30 × 10 = 300
Th ree hundred is our subtotal.
Now we multiply the numbers in the circles and then add the result
to our subtotal:
2 × 3 = 6
300 + 6 = 306
Our completed work should look like this:
20 18 × 17 = 15
–2
–3
300
- 6
306 Answer
Now let’s try the same example using 10 as a reference number:
+8
+7
10 18 × 17 =
Add crossways, then multiply by 10 to get a subtotal: