I recently took a dose calc exam in my maturity class. It is a very important test in the class and you have to pass with at least a 90% in order to move forward into the next class. So we can miss two questions before we fail. You get one retake and pretty much if you don't get the 90% you retake the class. It is not a hard exam at all it just has huge stakes.
So on my exam, the converting factor I used for inches to cm was 1in=2.54cm, which we know is correct. We never went over which conversion factors we should use, so imagine my surprise when I fail the test because what I should have used was 1in=2.5cm, and my answers were literally 1/100th of a decimal off.
My first thought was if anything, my answer is are MORE accurate.
I know I can retake the exam, but now the stakes are REALLY high. If I don't pass then I am screwed. I am really thinking of challenging this grade. It's already finals week and my anxiety is off the charts.
My only thought is that because the question was to one decimal place, they wanted you to use the conversion factor to one decimal place. As far as I know though, that's incorrect. You use the 2.54 and THEN round to the tenth place. To me, the correct answer is 50.3 cm
When I was in nursing school, it was routine for rounding rules to be used for imperial/metric conversions on all tests and exams, except in very rare circumstances. For instance, 2.54 cm (although precise) is generally rounded to 2.5 because if you look at a ruler or tape measurement tool, you are not going to find a marker for 2.54 cm. Likewise, you are not going to find a marker for .984 inches (using 2.5 cm as a starting point). ETA *You can identify 49.5 cm on a ruler or tape, you cannot identify 50.292 cm on a ruler or tape. The difference is negligible considering the baby's position and the original method of measurement. No two people would measure a moving baby the same way, at the same angle.
In the practice of nursing (like calculating the fluid intake of a patient), we use 1.0 ounce = 30 mL, even though the precise conversion factor from ounce to mL is 1.0 ounce = 29.57 mL, and 30 mL to ounce = 1.01442 ounces. This is an example of the rationale taught to me:
A patient in the US is not going to be drinking orange juice out of a vessel measured in mLs, but one measured in ounces. IV fluids will be measured in mLs. If you are calculating his intake, you can only do so as a close approximation because the orange juice (if he drank all of it) likely was not exactly 8 ounces, and the 500 mL of saline that just completed has a small amount of fluid remaining in the bag and line. The 'estimate' is still going to be an estimate no matter if you calculate the conversions precisely, or use the 'standard' rounding equivalency used in practice. You are going to report his intake as 740 mL (8 oz = 240 mL plus 500 mL saline = 740 mL), even though the precise calculation is 736.56 mL (8 oz = 236.56 mL plus 500 mL saline = 736.56 mL). The difference is small when compared to the volume (draw up 3.44 mL into a syringe and compare it to a bottle of wine).
Imperial to Metric, and Metric to Imperial conversions (in measurable units of distance, volume, and mass) do not equal one another. For the purpose of consistency in practice, negligible amounts of rounding is almost always used (except in some rare dosing situations).
5 mL = 1 tsp. (t)
(if exact, the calc would 5 mL = 1.01442 tsp, and the reverse conversion is 1 tsp. = 4.92892 mL)
15 mL = 1 tbsp. (T)
(if exact, the calc would be 15 mL = 1.01442 tbsp, and the reverse conversion is 1 tbsp. = 14.7868 mL)
30 mL = 1 oz
(if exact, the calc would be 30 mL = 1.01442 ounces, and the reverse conversion would be 1 ounce = 29.5735)
2.2 lbs = 1 kg
(if exact, the calc would be 2.2 lbs = .997903 kg, and the reverse conversion is 1 kg = 2.20462 lbs)
2.5 cm = 1 inch
(if exact, the calc would be 2.5 cm = .984252 inches, and the reverse conversion is 1 inch = 2.54 cm)
Your instructor should make clear the theories and expectations for your exam, and I would advise speaking to him/her about the issue as soon as possible. Be specific and ask for the conversion chart to use, and exactly how many decimal placements your answers should be for each question (i.e. Question 1 "round to the nearest 10th", Question 2 "round to the nearest 100th", etc.).
It is always easier to ensure you have the right information before you test than it is to appeal a missed question. Since you have a lot on the line, be proactive instead of reactive. It will help relax you and reduce test anxiety.
Thank you for posting the question; so they were looking to see 49.5 cm vs. 50.292 cm. We don't get any form of study guide or any idea for what type of questions; we are just told to study specific chapters and pages. BTW, I would ask if the decision/score can be repealed given 2.54 is more accurate, and they didn't provide a conversion chart.
Thank you.
And I'm sure there was probably a conversion table in those pages you had to read.
I wouldn't challenge it since you get another chance. Meet with the instructor and ask if you can go over the test. When you come across the 2.54 conversion problem ask if there was a specific conversion sheet you were supposed to use. Who knows the instructor might give you the point back after realizing you know how to do the problem and there wasn't a universal conversion sheet. If you come at the instructor trying to fight it, they put you on their list...
I wouldn't challenge it since you get another chance. Meet with the instructor and ask if you can go over the test. When you come across the 2.54 conversion problem ask if there was a specific conversion sheet you were supposed to use. Who knows the instructor might give you the point back after realizing you know how to do the problem and there wasn't a universal conversion sheet. If you come at the instructor trying to fight it, they put you on their list...
This.
ASK ASK ASK what they are looking for in terms if conversion in regards to inches; in my program we asked when a question like that popped up-which was rarely, but asked for clarification.
You may not get a similar question like that again because of conversion confusion, or it will be probably a totally different test; but at least clarify the rounding issue.
In any and all problems, rounding is never to be done until the end otherwise you introduce error.
Your teacher is a dunce.
Despite being a dunce, though, s/he holds your future in his/her hands. Go in there, butter him/her up, ask to enlightened to his/her sage and mystical ways, and then do what he/she wants.
He/she remains a dunce, though, and don't you believe for one second that he/she is anything besides completely wrong.
Remote...if you have talked with the school and they told you what you did wrong I would start studying and forget the past. it is done...time to move on. Learn from it and do what they want you to do. Good Luck!
I see your point and it's true that 2.54 is definitely more accurate and exacting.
However, your initial question states 19.8" so I would have stuck with matching decimals and dropped the .04 cm. In other words, match your significant figures past the decimal. I would still argue it, though. You can certainly round the 49.5 to 50 just as you can round down the 50.292 to 50. So.....you're pretty much right. It's also pretty shady they didn't give you the expected conversions!
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Carpediem1012, BSN, RN
315 Posts
My only thought is that because the question was to one decimal place, they wanted you to use the conversion factor to one decimal place. As far as I know though, that's incorrect. You use the 2.54 and THEN round to the tenth place. To me, the correct answer is 50.3 cm