Rounding To The Nearest 10 | 3th Grade | Khan Academy


Use a number line to round two-digit numbers to the nearest ten.

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31 thoughts

  1. I was taught in a physics class that if the final digit is a 5, it is rounded to the nearest even number. This way, approximately half the time it would be rounded up, half the time rounded down.

    For example, 35 would be rounded up to 40, and 45 would be rounded down to 40.

  2. There several different ways to handle the situation. Stores use the thumb rule or rounding to whatever benefits them the most. But the general way to do it in math from what i have been taught is just what Khan show. To round up if is 5 or above. Your way of doing it works to but is not a very well established practice. Of course it would have easier just did not use base 10 for our math. 😉

  3. There are a lot of different conventions used to round 5’s. Round to even, round to odd, round away from zero, round toward zero, round up, round down. Those are the six ways I know. Different situations prefer different conventions. If you look on the Wikipedia page for “Rounding” and go to the “Tie-breaking” section they talk about them in detail.

  4. Well, actually, it’s not the fact that it’s rounded to an even digit, but the fact that the rounding will be more evenly distributed.

    1,2,3,4 rounded down.
    5 rounded up approximately half the time, down the other times.
    6,7,8,9 rounded up.

    It would work exactly the same if you rounded final 5s to the nearest odd number.

  5. When you said that the final digit being a 5 is rounded to the nearest even number, you meant the nearest even number in the tens column, right?

    25 is rounded to 20, 35 is rounded to 40, 45 is rounded to 40. etc.

    That is what I meant by favouring the even digits. The even digits for the values 10x larger. Of course in physics experiments, getting an exact integer number shouldn’t occur at all, so it’s not a problem, but in applications that involve integers, the distribution isn’t constant.

  6. In physics class, we used the rounding trick when doing the math, usually rounding to the fourth decimal place. This simplified the calculations but maintained an acceptable degree of accuracy.

    We never rounded anything left of the decimal place. This may not have been the best Khan video to make this point, since he is dealing with rounding to 10. I only mentioned it as a general principle.

  7. I think that in any real world application where we would be rounding to the nearest ten, we’re either dealing with numbers orders of magnitude larger, the numbers are very crudely approximated already or we simply don’t care about accuracy. In all of these situations, I guess it wouldn’t really matter if the distribution of numbers is slightly skewed.

  8. It’s displaying this for me in 4th grade math even though it says “3th grade.” Anybody know why? Also, I know that “3th grade” isn’t correct and it should be “3rd” instead of “3th.”

  9. This is the dumbest shit ever.

    You round 5 to 10 simply because the community said so??? That doesn’t make sense because 5 is exactly half way. It doesn’t round to the nearest anything because it isn’t near anything, other than itself.

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