92 Speed Math for Kids
Th e completed problem looks like this:
+24
+2
+4
(10 × 12) 12 × 124 = 1,480
- 8
1,488 Answer
I try to choose reference numbers that keep both numbers either
above or below the reference numbers, so that I have an addition
rather than a subtraction at the end. For instance, if I had to multiply
9 times 83, I would choose 10 and 90 as reference numbers rather
than 10 and 80. Although both would work, I want to keep the
calculations as simple as possible.
Let’s calculate the answer using both combinations, so you can see
what happens.
First, we will use 10 and 90.
(10 × 9) 9 × 83 = 740
–1
–7 - 7
–9
747 Answer
Th at was straightforward. We multiplied 9 by 1 and wrote 9 in the
bottom circle. Th en we performed the following calculations:
83 – 9 = 74
74 × 10 = 740
1 × 7 = 7
740 + 7 = 747