If you always round up (or down) when the number ends in 5, you get a bias in a table of values. (So the total is biased high (or low), for example.) Better is to round to the nearest multiple of 20.

You say
“If the units are 5 or more, round up to the next whole ten.”
and
“55 to the nearest whole ten is 50”

Hello Keith
Thanks for the email. You spotted the (not quite deliberate) mistake which I have now rectified. I take your point about bias, especially in a long list of values. One of the main aims of rounding at this age is so that children can do quick mental calculations to check that their written answers or use of a calculator are sensible. They will quickly go on to round to the nearest 100 or 1000.
Thanks
Peter

## 2 Responses

If you always round up (or down) when the number ends in 5, you get a bias in a table of values. (So the total is biased high (or low), for example.) Better is to round to the nearest multiple of 20.

You say

“If the units are 5 or more, round up to the next whole ten.”

and

“55 to the nearest whole ten is 50”

But these do not agree.

Hello Keith

Thanks for the email. You spotted the (not quite deliberate) mistake which I have now rectified. I take your point about bias, especially in a long list of values. One of the main aims of rounding at this age is so that children can do quick mental calculations to check that their written answers or use of a calculator are sensible. They will quickly go on to round to the nearest 100 or 1000.

Thanks

Peter