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Rounding and estimation
Rounding and estimation

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1.2.1 Rounding to the nearest hundred

You will probably think to yourself that the coat shown costs about £300. £290 is considerably closer to £300 than it is to £200, so £300 is a reasonable approximation. In this case, 290 has been rounded up to 300. Similarly, 208 would be rounded down to 200 because it is closer to 200 than it is to 300. Both numbers have been rounded to the nearest hundred pounds.

When rounding to the nearest hundred, anything below fifty rounds down. So 248 rounds to 200. Anything over fifty rounds up. So 253 rounds to 300. Technically there is a problem with fifty itself as it is equidistant from the hundred above and the hundred below. Usually fifty is rounded up, so that a simple rule can be applied:

When rounding to the nearest hundred look at the tens digit:

  • if the tens digit is 0, 1, 2, 3, 4 round down;

  • if the tens digit is 5, 6, 7, 8, 9 round up.

So £284 rounds up (to £300) and £233 rounds down (to £200).