11 Plus Exams Forum

hi all

i hope that somebody can explain this maths problem to me

0.1 x 0.1 = 0.01

how can this be?

i thought the rule was always that multiplying or adding something makes the number bigger - but the answer to 0.1 x 0.1 is 0.01 which is a smaller number

how can this be?

can anybody explain this to me as it is baffling me

many thanks X

inonothing

I'll try....

If you multiply a number by a decimal, you make it smaller.

For example, 0.5 is 1/2 (a half) so if you multiply 2 by 0.5 you are working out what half of 2 is so

0.5 x 2 = 1

In your example, think of 0.1 as 1/10 or one tenth. You need to find out what one tenth of one tenth is so the answer must be smaller than one tenth.

Hope that helps!?

If you convert 0.1 into a fraction ie 1/10 instead, it makes it easier to visualise what is happening. When you multiply something by 1/10 what you are actually doing is multiplying it by 1 and dividing it by 10 hence the reason it is getting smaller as a result of a multiplication.

1/10 x 1/10 = 1/100 which in decimals is 0.01.

I hope this helps but I'm sure someone will be along with a better explanation soon.

CN

The above give the correct idea as to why the answer becomes smaller.

The actual arithmetical process is quite easy.

0.1 x 0.1

For the moment ignore the decimals and just multiply the numbers

1 x 1 = 1

Now look at the total number of decimal places in the original equation, that is the total number of digits in the two numbers to the right of the decimal point. The total is 2 decimal places

0.1 (1 digit to the right) x 0.1 (1 digit to the right)

Therefore the final answer will have 2 decimal places, or two digits to the right of the decimal point.

1 x 1 = 1

0.1 x 0.1 = 0.01

0.2 x 0.2 = 0.04

0.2 x 0.02 = 0.004

2.1 x 0.02 = 0.042

If you think of 0.1 at one tenth, then the sum is

one tenth * one tenth

or one tenth of one tenth

which is one hundredth (or 0.01)

INONOTHING wrote: i thought the rule was always that multiplying or adding something makes the number bigger - but the answer to 0.1 x 0.1 is 0.01 which is a smaller number

how can this be?

can anybody explain this to me as it is baffling me

many thanks X

inonothing

imagine a bar of chocolate with 10 squares.

0.1 =1/10 so 1/10 of the bar is 1 measly square!

now cut this square into 10 pieces again, (so you hava tenth of a tenth of a bar)
you get even less chocolate.

INONOTHING wrote:i thought the rule was always that multiplying or adding something makes the number bigger

Nope. That's not a rule in maths.
Adding a positive thing to a something makes it bigger, adding a negative thing to a thing makes it smaller.
Multiplying a thing by something bigger than 1 makes it bigger (numerically), mutlipying a thing by something smaller than 1 makes it smaller.
Multiplying a thing by something negative makes it negative, unless it's already negative, in which case it becomes positive.