24 Speed Math for Kids
Test you rself
Now try these problems by yourself.
a) 12 × 15 = f) 12 × 16 =
b) 13 × 14 = g) 14 × 14 =
c) 12 × 12 = h) 15 × 15 =
d) 13 × 13 = i) 12 × 18 =
e) 12 × 14 = j) 16 × 14 =
The answers are:
a) 180 b) 182 c) 144 d) 169
e) 168 f) 192 g) 196 h) 225
i) 216 j) 224
If any of your answers were wrong, read through this section again,
fi nd your mistake, then try again.
How would you solve 13 × 21? Let’s try it:
10 13 × 21 =
We still use a reference number of 10. Both numbers are above 10,
so we put the circles above. Th irteen is 3 above 10, 21 is 11 above,
so we write 3 and 11 in the circles.
Twenty-one plus 3 is 24, times 10 is 240. Th ree times 11 is 33, added
to 240 makes 273. Th is is how the completed problem looks:
+3
+11
(^10) 13 × 21 = 240
- 33
273 Answer