Rounding Decimals

Rounding keeps a number short while staying close to it. To round 5.6382 to two decimal places, keep two digits after the point, 5.63, and look at the next digit, the 8. It is 5 or more, so the last kept digit goes up by one: 5.64.

If the next digit is 4 or less, the kept digits stay as they are: 2.871 rounded to two places is 2.87. Either way, everything after the kept places is dropped. The rule answers one question: is the number nearer the value just below or just above? Past halfway the higher value is the nearer one. Exactly halfway, as in 2.875 to two places, both are equally near, and the usual rule is to round up, so a next digit of 5 or more rounds up.

Two decimal places means the same as the nearest hundredth, which is how prices are rounded to whole cents. Only the digit right after the kept places counts, so look at that one digit and ignore the rest. On the board, write the rounded value with a letter, like r = 5.64.