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Discussion

Math help! When to round up.

When can you round up on a dosage problem?

Why can you round 0.75mls to 0.8mls but cannot round 2.5mls. I know you round to the nearest tenth.... isn't the tenth spot the first number after the decimal or do I have it all wrong?

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  • Experts

I think there is a practical side to these answers that has to be considered as well. If you are calculating the amount of a solution to draw up into a syringe, you can draw up 2.5 mL because a syringe has a 2.5 marking on it. Most syringes have 0.1mL increment marks on them. It does not, however, have a 0.75mL marking. You have to round to 0.8mL and draw to the 0.8mL marking. So, seeing the equipment you are going to use might help.

It's the same with drops. There is no such thing as a 2.5 drop of anything. There are only whole numbers of drops.

Same with tablets. Some tablets are scored and can be broken in half, so 1.5 tablets is an acceptable answer in some cases. Some pills are never supposed to be broken, so only a whole number answer will do for them. In these cases, looking at a drug book and how a drug is supplied is going to help out.

Why can you round 0.75mls to 0.8mls but cannot round 2.5mls. I know you round to the nearest tenth.... isn't the tenth spot the first number after the decimal or do I have it all wrong?

Rounding 0.75 to 0.80 is rounding by 0.05 (the hundredths place) which represents a change of 6.7%

Rounding 2.5 to 3.0 is rounding by 0.5 (the tenths place) which represents a change of 20%

In the latter case, you're introducing nearly three times the variation from the nominal amount as you are in the former case.

  • Author

I understand that rounding 2.5mls to 3mls is giving more medication that required. Our instructors tell us to round to the nearest tenth spot....I guess that is what is messing me up!

I understand that rounding 2.5mls to 3mls is giving more medication that required. Our instructors tell us to round to the nearest tenth spot....I guess that is what is messing me up!

You are correct that the "tenths" spot is the first one to the right of the decimal.

With 2.5, the tenths spot is 5. It can't be "rounded". The ones place could be rounded up to 3 or down to 2.

With 0.75, the tenths spot is 7 and can be rounded up to 8 by eliminating the hundredths spot (5) resulting in 0.8

I'm not explaining this very well in writing. Perhaps this is the way to put it:

To round in the tenths place, you must have a value in the hundredths place. In general, to round in a given position, there must be a value in the position one place to the right.

  • Author

One value to the right of the tenths spot makes sense!....thank you so much!

One value to the right of the tenths spot makes sense!....thank you so much!

You're welcome!

BTW, make sure you understand Daytonite's "practical side" of the question. It helps to address the WHY behind the WHAT that your instructors are telling you.

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