Rounding decimals.

Mike · Post by **Mike** » Fri Jul 10, 2009 1:02 pm

Hi

3.25487

To round to 2 decimal places, it is correct to say that you round up or down based on the number on the right, but it is the number on the immediate right not the number on the far right.

The first 2 decimal places gives 3.25

leaving 0.00487

The number that determines the rounding up or down is

0.004

not

0.00007

The rule then is that if the next number is 5,6,7,8 or 9 then round up, if it is 0,1,2,3 or 4 then round down.

As the next number is 4, then round down, giving 3.25.

The problem with the incorrect replies concerns irrational numbers that cannot be written as a decimal, such as the value of pi. There is no extreme right number available to determine the rounding value.

Regards

Mike

dadofkent · Post by **dadofkent** » Fri Jul 10, 2009 5:25 pm

dadofkent wrote:
hermanmunster wrote:3.25

ow got something in my eye
Thankyou Hermanmunster. I am up against a year 5 top set maths teacher, not to mention a wife, who say you round from the right, and not from the left, and which would give a value of 3.26.

Just to clarify, when I said from the right I meant the far right, and then work backwards, and for from the left, I meant the left, or first, of the redundant digits, i.e you round up/down according to the value of the first of the digits after the reqired no. of decimal plasces.

Bexley Mum 2 · Post by **Bexley Mum 2** » Fri Jul 10, 2009 6:02 pm

Well, I'm pleased to say that I asked my 3 DSs this question - separately. They all said 3.25 without hesitation. Glad someone is teaching them right!

Guest55 · Post by **Guest55** » Fri Jul 10, 2009 6:54 pm

http://www.cimt.plymouth.ac.uk/projects ... k8_4i5.htm

This might help.