ffirs.indd

Multiplying Above & Below the Reference Number 33
Mathematically, we would say: when we multiply two positive (plus)
numbers, we get a positive (plus) answer. When we multiply two
negative (minus) numbers, we get a positive (plus) answer. When
we multiply a positive (plus) by a negative (minus), we get a minus
answer.
Let’s try another problem. Would our method work for multiplying
8 × 42? Let’s try it.
We choose a reference number of 10. Eight is 2 below 10 and 42 is
32 above 10.
+32
10 8 × 42 =
–2
We either take 2 from 42 or add 32 to 8. Two from 42 is 40, times
the reference number, 10, is 400. Minus 2 times 32 is –64. To take
64 from 400 we take 100, which equals 300, then give back 36
for a fi nal answer of 336. (We will look at an easy way to subtract
numbers from 100 in the chapter on subtraction.)
Our completed problem looks like this:
+32
10 8 × 42 = 400 – 64 = 336 Answer
–2
36
We haven’t fi nished with multiplication yet, but we can take a rest
here and practice what we have already learned. If some problems
don’t seem to work out easily, don’t worry; we still have more to
cover.
In the next chapter we will have a look at a simple method for
checking answers.