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102 Speed Math for Kids
We multiply 4 by 3¼ to get 13 (4 × 3 = 12, plus a quarter of 4
gives another 1, making 13). Write 13 in a circle below the 4,
under 96.
(100 × 3¼) 96 × 321 =
–4
–4
–13
Subtract crossways.
321 – 13 = 308
Multiply 308 by the base reference number of 100 to get 30,800.
Th en multiply the numbers in the circles.
4 × 4 = 16
Th en:
30,800 + 16 = 30,816 Answer
Th at can easily be done in your head, and is most impressive.
USING DECIMAL FRACTIONS
AS REFERENCE NUMBERS
Here is another variation for using two reference numbers. Th e
second reference number can be expressed as a decimal fraction of
the fi rst. Let’s try it with 58 times 98. We will use reference numbers
of 100 and 60, expressed as 0.6 of 100.
(100 × 0.6) 98 × 58 =
Th e circles go below in each case. Write 2 inside both circles.
Multiply 2 times the multiplication factor of 0.6. Th e answer is 1.2.
All we do is multiply 6 times 2 to get 12, and divide by 10.