secrets-of-mental-math-malestrom

98
Secrets of Mental Math
You can even put this trick to use in the middle of a problem.
If your fraction is 3
16 , look what happens:
.1
163.000
16
14
Once the problem is reduced to 1 4
16 , you can further reduce it
to 7 8 , which you know to be .875. Thus 3
16
.1875.
EXERCISE: DECIMALIZATION
To solve the following problems, don’t forget to employ the various
one-digit fractions you already know as decimals. Wherever
appropriate, simplify the fraction before converting it to a
decimal.
1.
2 5 2.
4 7 3.
3 8 4.
9
1 2
5.
5
1 2
6.
6
1 1
7.
1
4
24
8.
1
3
27
9.
1
8
48
10.
1
0
14
11.
6
3 2
12.
1
9
45
TESTING FOR DIVISIBILITY
In the last section, we saw how division problems could be simplified
when both numbers were divisible by a common factor.
We end this chapter with a brief discussion of how to determine
whether one number is a factor of another number. Being able
to find the factors of a number helps us simplify division problems
and can speed up many multiplication problems. This will
also be a very useful tool when we get to advanced multiplication,
as you will often be looking for ways to factor a two-,