secrets-of-mental-math-malestrom

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Secrets of Mental Math
Let’s try a similar division problem using the same method of
mental computation:
675 8
As before, since 675 falls between 8 10 80 and 8 100
800, your answer must be below 100 and therefore is a twodigit
number. To divide 8 into 675, notice that 8 80 640
and 8 90 720. Therefore, your answer is 80 something.
But what is that “something”? To find out, subtract 640 from
675 for a remainder of 35. After saying the 80, our problem
has been reduced to 35 8. Since 8 4 32, the final answer
is 84 with a remainder of 3, or 84 3 8 . We illustrate this problem
as follows:
84
8675
640
35
32
3
remainder
3
Answer: 84 with a remainder of 3, or 84 8
Like most mental calculations, division can be thought of as a
process of simplification. The more you calculate, the simpler
the problem becomes. What began as 675 8 was simplified to
a smaller problem, 35 8.
Now let’s try a division problem that results in a three-digit
answer:
947 4