When rounding to preserve significant figures, why is it that when the digit removed is 5, the preceding number is increased by 1 if it is odd and remains unchanged if it is even? For example, what is the logic in rounding 17.71 to 17.8, but 17.79 to 17.7? Clearly, that is unreasonable!
2007-09-08 16:30:27 · 8 answers · asked by cartonboy 2 in Science & Mathematics ➔ Mathematics
You have stated the rule incorrectly. And it is one of at least two equally good rounding rules.
It should read something like this:
a. If the last digit is less than five, drop it.
b. If the last digit is more than five, drop it and increase the second to last digit by one.
c. If the last digit is equal to five, drop the five and increase the second to last digit by one if it is odd, and do not increase the second to the last digit if it is even.
Using this rounding rule, 17.75 rounds to 17.8, and 17.85 also rounds to 17.8.
17.71 would round to 17.7, not 17.8; and 17.79 would round to 17.8, not 17.7.
2007-09-08 16:44:55 · answer #1 · answered by Boots McGraw 5 · 2⤊ 0⤋
Rounding .5 up to 1 makes sense because if you have half or more than you might as well have a full unit.
I have never heard the rule you're speaking of. In your example, 17.71 would be rounded to either 17.7 or 18 depending on the degree of accuracy you're looking for. Similarly, 17.79 would be rounded to either 17.8 or 18.
2007-09-08 16:38:19 · answer #2 · answered by Justin H 7 · 0⤊ 0⤋
17.71 would round to 17.7
while 17.79 would round to 17.8
You round for many reasons, but whether you round up or down depends on how large the number is. 5 -9 are larger numbers, making it closer to 1 larger. While 1 - 4 are smaller numbers making it closer to the lower whole, or part.
Yet, when it comes to $, every place rounds up 1. So, if you buy an item and with tax it comes to $12.112, they;ll round it up to $12.12. Otherwise in just plain math, it is a time saver and a choice. Do you realy want to add or mulitply together numbers to the tens of thousandths?
2007-09-08 16:40:31 · answer #3 · answered by Melissa 3 · 0⤊ 0⤋
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2016-12-13 03:49:50 · answer #4 · answered by ? 4 · 0⤊ 0⤋
Errrmmmm............ I think you have the rounding rules a bit mixed up. 17.79 rounds to 17.8 and 17.71 rounds to 17.7
HTH
Doug
2007-09-08 16:38:37 · answer #5 · answered by doug_donaghue 7 · 0⤊ 0⤋
17.71 rounded the nearest tenth would be 17.8. rounded to the nearest hundredths would be 17.70. depending on wich digit. if 5 or more round up. 4 or lower round down.
I think.
2007-09-08 16:39:29 · answer #6 · answered by Ham8888888888 3 · 0⤊ 0⤋
I don't know what rounding rule YOU are using in your examples, but you better find another one.
2007-09-08 16:36:12 · answer #7 · answered by cattbarf 7 · 1⤊ 0⤋
In your example following the rounding rule, you would round the number up one if the number next to it is greater than five. If the number is less than five, round the number down.
Like this.
17.71 would be rounded down to 17.69
17.79 would be rounded up to 17.80
2007-09-08 16:34:46 · answer #8 · answered by Lord of Chaos 4 · 0⤊ 3⤋