Rounding and estimating question

[Melinda S in TX]

Dd understands how to round and estimate. What we don't know is what to round to. Her lesson today says to round to the nearest thousands or hundreds. If you had a problem like 5,698+1,394 would you round the to the nearest hundred or thousand? How do you decide which one, or does it matter?

 

Blessings,

Melinda

[Capt_Uhura]

I just saw something in Math Mammoth which was interesting. I've always been taught if it's 5 or over you round up, if not, round down. In MM, you take into account how much error you will have. For example, if you round both numbers up, you tend to get higher error. In the problem my friend showed me, it was 45 + 79. Instead of rounding to 50 and 80 getting 130 w/ error being 130-124=6, you'd round to 40 and 80 getting 120 and your error being 124-120=4. This is a very simplistic example but I had never seen that before.

 

 

I'm probably not helping you. So the problem says you can round either to the thousands or hundreds place? It would depend on how close you wanted to be. Rounding to the nearest hundreds gets you a more accurate answer.5700+1400=7100 for error of estimation of 8. If you round each to the thousands 6000+1000=7000 for an error of estimation of 92.

 

Which program is this from?

[Mallory]

I would round these to 100's because they are both really close to the next hundred. But if it doesn't say I don't think it matters (although if it were my kids assignment, I might make them do both).

[NanceXToo]

I don't think it matters. It's up to you if it doesn't specify! Does she need more work with rounding hundreds, or rounding thousands? You could always do both, or mix it up and alternate if there are several problems like that.

[Mallory]

I've been thinking about this some more.

 

I always think it is nice to see the connections to real life in math.

 

If these were numbers I was using for something in my real life that I had to add (and quite frankly I find the math I use every day to be almost all estimating- how much the groceries in my cart cost, how much stain I need for the fence, how much gas I'll need for the month, etc.) I would stick by my previous recomendation to round to 100's.

 

I also can see how rounding by the 100's in this case leads to an easier way to add these and get an exact answer. It is easier to add 57 (00) and 14 (00) and subtract 8 then to add 5698 and 1394.

[Lolly]

A lot of problems, especially in elementary, want the children to front end round. That would be rounding to the highest place value. For 5,698+1,394 you would round both to the thousands. For something like 2,345+566, you would round the first number to the thousands and the second to the hundreds.

[Tylianna]

Is there a teacher's manual to see what the answer is?

[Chris in VA]

A lot of problems, especially in elementary, want the children to front end round. That would be rounding to the highest place value. For 5,698+1,394 you would round both to the thousands. For something like 2,345+566, you would round the first number to the thousands and the second to the hundreds.

 

This. It's called front end estimation in dd's school. The idea is to be quick--not necessarily accurate. In the OP's example, it would take too long to add the numbers if they were rounded to the nearest hundred.