162 Speed Math for Kids
Th e problem now looks like this:
32
–2
- 5
30 24.^3010
Th is is not diffi cult, but you need to keep in mind that you have to
allow for the subtraction from the remainder.
REVERSE TECHNIQUE – ROUNDING OFF UPWARD
Let’s see how direct long division works for dividing by numbers
with a high units digit, such as 39. We would round the 39 upward
to 40. For example, let’s divide 231 by 39. We set up the problem
like this:
39
+1
40 231
We divide both numbers by 10, so 231 becomes 23.1 and 40
becomes 4. Four won’t divide into 2, so we divide 4 into 23. Four
divides 5 times into 23 with 3 remainder (4 × 5 = 20). We carry the 3
remainder to the next digit, 1, making 31. Our work looks like this:
39
+1
5
40 23.^31
We correct our remainder for 39 instead of 40 by adding 5 times
the 1, which we added to make 40.
5 × 1 = 5
31 + 5 = 36