Is there a general rule for how to round numbers?

[Night Elf]

I was always taught that if specific instructions were not given, I should always round to the highest place value. So 136 would be 100. DH disagrees and says he would round it to 140. So what about a number like 1795? I say 2000. DH says 1800.

 

And what about decimals? 72.418 Does that round to 73? 72.4? 72.42?

[lionfamily1999]

5 rounds up, 4 rounds down.

 

With decimals, it depends on what you're going for... If the goal is a whole number, then you take the tenths and round accordingly. IOW, you only use the next place to determine your estimate. If you are rounding to tens you use the ones, if you're rounding whole numbers you use tenths. Rounding to thousands you use the hundreds.

[LaxMom]

It depends on what you're rounding to: nearest thousand? nearest hundred? nearest whole number, nearest tenth?

 

So, 1795 rounded to the nearest hundred would be 1800, to the nearest thousand, 2000. (and that would depend on what I was estimating... mileage would be rounded to the nearest hundred. Cost of kitchen remodel? Nearest thousand)

 

72.418 would be 72.4 rounded to the tenth, 72 to the nearest whole number.

 

You're just rounding to different points. ;)

[rlowetx]

Not to confuse matters, but with a computer program my husband and I designed we had to build it to round up.. for .51, and down for .5 - the first time we ever did that.. Apparently the standard 5 goes up and 4 goes down didn't cover contract language and calculating pricing.. ;-)

 

Still, up until then the program always rounded .5 up and .4 down and we only had 1 client that did it that way.. weird.

[unsinkable]

I only round numbers who are already comfortable with their bodies.

[KidsHappen]

You are just rounding to different places. I tend to be more exact and would round like your hubby. I have one dd who would round say time to the nearest hour or so and another is rounds to the nearest minute. It is 6:06 right now, not 6:00 or even 6:05 but 6:06. Everyone's different.

[Night Elf]

Yes indeed. I understand all these points. What I don't get is how to choose what place value to round to when you are not specifically told what to do.

 

If it just says round the following: 7438, without specifically saying to round it to the nearest ten, hundred, or thousand. I would round it to 7000 but my DH would round it to 7400. I know it's all estimation but the answers in a textbook don't seem to account for multiple possibilities. Then the only way we know the correct answer is to look it up in the answer key. I can't see that being helpful when the children are taking a test.

 

But I guess it's something very minor and likely worth the stress. I'd prefer my dd skip those questions on her upcoming test. I find the problems too vague.

[Brenda in FL]

Yes indeed. I understand all these points. What I don't get is how to choose what place value to round to when you are not specifically told what to do.

 

If it just says round the following: 7438, without specifically saying to round it to the nearest ten, hundred, or thousand. I would round it to 7000 but my DH would round it to 7400. I know it's all estimation but the answers in a textbook don't seem to account for multiple possibilities. Then the only way we know the correct answer is to look it up in the answer key. I can't see that being helpful when the children are taking a test.

 

But I guess it's something very minor and likely worth the stress. I'd prefer my dd skip those questions on her upcoming test. I find the problems too vague.

 

Anytime I've seen this, the text has always specified what place value to round to. Are the answers in your text consistent? If so, I'd just use that, but if its different each time and the problem doesn't specify which place value to round to, then I'd be contacting the publisher for clarification. How frustrating!

[petepie2]

Yes indeed. I understand all these points. What I don't get is how to choose what place value to round to when you are not specifically told what to do.

 

If it just says round the following: 7438, without specifically saying to round it to the nearest ten, hundred, or thousand. I would round it to 7000 but my DH would round it to 7400. I know it's all estimation but the answers in a textbook don't seem to account for multiple possibilities. Then the only way we know the correct answer is to look it up in the answer key. I can't see that being helpful when the children are taking a test.

 

But I guess it's something very minor and likely worth the stress. I'd prefer my dd skip those questions on her upcoming test. I find the problems too vague.

 

Are these problems from a math book or are they part of word problems or science problems?? I remember in science you have to use "significant digits". In other words, your answer can't be any more accurate than the numbers that you were given in the problem. So that would determine to what place value you would need to round.

[Unicorn.]

Yes indeed. I understand all these points. What I don't get is how to choose what place value to round to when you are not specifically told what to do.

 

If it just says round the following: 7438, without specifically saying to round it to the nearest ten, hundred, or thousand. I would round it to 7000 but my DH would round it to 7400. I know it's all estimation but the answers in a textbook don't seem to account for multiple possibilities. Then the only way we know the correct answer is to look it up in the answer key. I can't see that being helpful when the children are taking a test.

 

But I guess it's something very minor and likely worth the stress. I'd prefer my dd skip those questions on her upcoming test. I find the problems too vague.

 

In that case, I'm w/ you. I would round to 7000 also. I don't know why. :D

[joannqn]

Anytime I've seen this, the text has always specified what place value to round to. Are the answers in your text consistent? If so, I'd just use that, but if its different each time and the problem doesn't specify which place value to round to, then I'd be contacting the publisher for clarification. How frustrating!

 

:iagree:

 

The text should specify. If it doesn't, I'd mark the answer correct if they rounded correctly regardless of which place value they rounded to.

 

Are these problems from a math book or are they part of word problems or science problems?? I remember in science you have to use "significant digits". In other words, your answer can't be any more accurate than the numbers that you were given in the problem. So that would determine to what place value you would need to round.

 

:iagree:

 

The text should specify unless it is science. In that case, you'd round per the rules of significant digits.

[KidsHappen]

I tend to use the 5 up, 4 down rule on the second number in the squence when it is unspecified. So 678, 554 I would use the ten thoudands place and since it is 7, I would rule up so the number would be 680,000. I try to round as close to the actual value possible.

[Night Elf]

My dd11 is just finishing Progress in Mathematics as her K12 5th grade math textbook.

 

We just skip it and move on. She knows the general rule about rounding and that is all that matters. I have reminded her many times to read the directions before doing any assignment. If the directions are unclear, it is not her fault.