Calculating where the decimal point should be

[Andy]

Hi,

Well I've now managed multiplication of very large number which works well.

I am however lost on where the decimal point should be in the result when both numbers to be multiplied together have decimal points in them.

e.g. 123456.12345 x 8.1234 = answer with 5 decimal placed digits.
      123456.12345 x 8.12345 = answer with 5 decimal placed digits.
      123456.12345 x 8.123456 = answer with 5 decimal placed digits.
      123456.12345 x 8.1234567 = answer with 4 decimal placed digits.
      123456.12345 x 8.12345678 = answer with 5 decimal placed digits.

Anyone good at maths that can explain this and if so, how do I work out how many decimal places should be in my multiplication answer?

Thanks,
Andy.


     

[Andy]

Okay,

I've got it, I was using an online calculator which wasn't giving all the decimal places, also the windows scientific calculator gets the decimals wrong too!

So the correct answer is to add the number of decimal places in each number together and that is how many decimal places you need.

e.g. number 1 has 2 decimal places, number 2 has 4 decimal places = answer with 6 decimal places.

Andy.