2: Multiplication can Increase or Decrease a Number
Question: Does multiplication always increase a number?
Further Explanation
So, multiplying can have a reducing effect when multiplying a positive number by a fraction
which is less than one. But this can still be confusing. While we accept the above, the
concept of 'a number times 8' continues to be perceived as an increase. How then can we
attach a meaning to 1
2
´ 8 so that this will be perceived as decreasing?
When multiplying by a whole positive number, e.g. 6 times 5, we understand this as being
5 added over and over again, how ever many times – six times in this example. But this
interpretation of times does not quite work with fractions. If we ask how many times, the
answer is "not quite once".
Again we need to put the term multiplying into a context with which we can identify, and
which will then make the situation meaningful.
We want to buy 30 roses which are sold in bunches of 5, so we ask for "6 of the 5-rose
bunches". In this way, the word times also often means of. If we try using the word of
when times appears to have an unclear meaning, we get 1
2
of 8 rather than 1
2
times 8.
Indeed we know what 1
2
of 8 means – namely 4.
Misconception
Yes it does; take the number 8, for
example:
2 8 16
3 8 24
4 8 32
´ =
´ =
´ =
etc.
In each it is getting larger, so, yes,
multiplication clearly increases a
number.
Correct
No – it increases a number only under
certain conditions.
Multiplying any positive number by a
whole number greater than 1 will always
increase its value – see the example
opposite; but consider
1
2
´ 8 = 4 ; here the number 8 is reduced.
0 4 8 12 16 20 24 28 32
ß
12
´ 8
ß
2 ´ 8
ß
3 ´ 8
ß
4 ´ 8
numbers
smaller
than 8
numbers
larger
than 8