60 Speed Math for Kids
Is there a way to make the method work in this case? Th ere is, but
we must use a diff erent reference number. Th e problem is not with
the method but with the choice of reference number.
Let’s try a reference number of 5. Five equals 10 divided by 2, or
half of 10. Th e easy way to multiply by 5 is to multiply by 10 and
halve the answer.
+1
5 6 × 4 =
–1
Six is higher than 5, so we put the circle above. Four is lower than 5,
so we put the circle below. Six is 1 higher than 5, and 4 is 1 lower,
so we put 1 in each circle.
We add or subtract crossways:
6 – 1 = 5
or
4 + 1 = 5
We multiply 5 by the reference number, which is also 5.
To do this, we multiply by 10, which gives us 50, and then divide by
2, which gives us 25. Now we multiply the numbers in the circles:
1 × –1 = –1
Because the result is a negative number, we subtract it from our
subtotal rather than add it:
brent
(Brent)
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