Rounding up or rounding down

Question

Hello,

I am not 100% sure whether to round up an integer, say 2.5, to 3.0 or round down to 2.0. And what should happen in case of -2.5?
Does such situation occur on GMAT?

Please respond.

Bunuel · Accepted Answer

Rounding is simplifying a number to a certain place value. To round the decimal drop the extra decimal places, and if the first dropped digit is 5 or greater, round up the last digit that you keep. If the first dropped digit is 4 or smaller, round down (keep the same) the last digit that you keep.

Example: 
5.3485 rounded to the nearest tenth = 5.3, since the dropped 4 is less than 5.
5.3485 rounded to the nearest hundredth = 5.35, since the dropped 8 is greater than 5.
5.3485 rounded to the nearest thousandth = 5.349, since the dropped 5 is equal to 5.

So 2.5 rounded to the nearest integer equals to 3.

As for rounding negative numbers: you won't need this for GMAT, so don't worry about it.

u0422811 · Answer

I always adhere to the rule of 5, if its .5 or above you round up. This is obviously inverse for negative numbers.

You may encounter this but its unlikely as most interaction with strictly integers is limited to data sufficiency and you do not need to actually solve these only prove that they can be solved.

mandhan · Answer

Thanks u0422811 and Bunuel.

FQ · Answer

I believe the official rule of gmat is to round up if its .5 or above and down if its .4 or below. Though one must be carefull in some instances where you must round down at all times. For example if the question asks the number of people that can fit into a room, and your calculation gives 11.9, the answer would be 11 rather than 12.

jpr200012 · Answer

The GMAT will occasionally give a crazy rule for rounding, and say any number   should always be rounded up/down. They usually rely on "tricking" you on negative numbers. When rounding up/down on a negative number, it may be helpful to visualize the number line to make sure you are rounding in the right direction!

bullseye800 · Answer

There is a theory in maths....which says if you are rounding about a odd no. and the next digit is 5....we move up...and if its even then we move down

the idea is once a set of random numbers is rounded the overall figure should be closer to the earlier sum (without rounding), the usual round up around 5 is upward biased

Any experts take on this?

Would like to know this exact rule and does gmat take this rule or simple 5up rule....if so could u provide an OG example which clarifies this?

Thanks

Bunuel · Answer

Rounding rules used for the GMAT are given in my post above. No need to complicate things.

bgpower · Answer

Bunuel,

I'm slightly confused by your explanation and the GC Math Book. IMO, in example 1 regardless of the fact that you should round to the nearest tenth, you should always start backwards, basically that the ten-thousandth makes the 8 become a 9, then this thousandth changes the 4 to a 5, and finally the 5 transforms the tenth in a 4. At least that is the rule I have studied in primary school. I don't argue that your rule may be the one applicable on the GMAT, but nevertheless, I would be glad to hear your take on this. Thank you!

Bunuel · Answer

The GMAT uses the rule given in my post. When rounding to the tenth you look at only the hundredth digit, when rounding to the hundredth you look at only the thousandth digit, etc.

IanStewart · Answer

You will never need to worry about how to round 2.5 "to the nearest integer" on the GMAT. Different conventions are used in different countries in this situation, so it would not be a fair question. I'd personally have no idea how to answer it. It's a question that doesn't really make any sense - we can't round 2.5 to the "nearest integer", because two different integers (2 and 3) are equally near to 2.5.

That said, you would definitely round 2.5001 up to 3 (if rounding to the nearest integer), because 2.5001 is (very slightly) closer to 3 than it is to 2. Similarly, you'd round 2.4999 down to 2, because 2.4999 is (very slightly) closer to 2 than it is to 3. That's exactly what you'd do if you followed the rule Bunuel described above, so that rule is a perfectly good one to follow.

bumpbot · Answer

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Rounding up or rounding down

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Rounding up or rounding down

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