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Rounding
By Caroline Dod (T471) on Sunday, November 14, 1999 - 04:04 pm:

My class of year 3/4 children would like to know why we round numbers ending in 5 up eg 55 to 60, rather than 55 to 50.

By Chris Jefferson (Caj30) on Sunday, November 14, 1999 - 04:17 pm:

Well, partly it is just because we need to decide some way of doing it. However, here is another reason.
Obviously, 0.4 -> 0, 0.6 -> 1
Also,
0.499 -> 0
0.501 -> 1
So if we say 'everything that starts with 5 goes up' it makes things easier. The only part you may have to consider is 0.500 which you may as well put up with everthing else.
Chris

By Andrew Wyld (Acew2) on Friday, November 19, 1999 - 04:55 pm:

Hi there!

In addition, I thought I could add a possible motivation for rounding up rather than down. Think of a digital watch which shows only minutes, not seconds (almost all digital watches were like this when they first came out). Then said watch will say 12:05 from 12:05:00 to 12:05:59. In other words, from the watch display, the instant before 12:06 is indistiguishable from the exact instant of 12:05. To the nearest ten minutes, (almost) 12:06 is clearly 12:10. However, we haven't access to the information about seconds, so we have to assume that there may be "lost digits", as it were, and this is a good reason for always rounding 12:05 to 12:10 (nearest ten minutes).

I hope this is useful - I haven't put it very well, but I hope it meets your need!

Andrew Wyld