Hi all, I've run into a problem just a few times with using pi. Most of the time I can round to 3 for my calculations and I'm fine. Twice, though, rounding to 3 actually led me to an incorrect answer. Using 3.14 all the time is rather arduous, but using 3 isn't 100% reliable. Sometimes it is obvious from the question that you can or can't round, but that wasn't the case for either of the problems I got wrong here. Am I the only one with this problem? How do you handle pi? I know it's unlikely to affect my score on test day, but in the spirit of covering all my bases I thought I'd ask. (I did a search and didn't come up with anything so apologies if there's another thread on this.)
Dealing with pi on the MCAT
- Thread starter janmcat
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I have not really come across any problems where I had to use pi. A lot of passages I have done that involve a radius phrase the answer choices in terms of pi.
I would personally try 3 and if the answers are close, just use 3.15.
I would personally try 3 and if the answers are close, just use 3.15.
Thanks! In this case the answers weren't close. The problem was that we were dealing with very large numbers so the 0.14 discrepancy just grew and grew, if that makes sense. But I couldn't "simplify" the larger numbers either in the context of the question. The answer key didn't show the calculation either. Oh well, if nobody else has had this problem I'll chalk it up to a quirk and move on. Thanks again!
One was from the TPR Physics book, Ch. 4. The question requires you to determine the velocity of a yo-yo, which is (1.8)(pi)(3) and then use that in the centripetal acceleration equation, (v^2)/r.
If you use 3 for pi you get 16.2 for v, which you then have to square and divide by 0.9, giving an answer of 290ish.
If you use 3.14 for pi you get 16.96 for v (essentially 17) which you then square and divide by 0.9, giving an answer of 320ish.
One answer choice was 284 and one was 320. I chose 284 (290 is so much closer to 284 than 320!) but the answer was 320.
I should have realized that my answer would have had to have been low. Since I rounded down, there was no way for my answer to be greater than the real answer, so 284 couldn't have been the correct answer. But it did get me, and since I'm at the beginning of my MCAT prep I thought this might be a "thing" that others have dealt with before. Apparently not. Good luck with your MCAT!
If you use 3 for pi you get 16.2 for v, which you then have to square and divide by 0.9, giving an answer of 290ish.
If you use 3.14 for pi you get 16.96 for v (essentially 17) which you then square and divide by 0.9, giving an answer of 320ish.
One answer choice was 284 and one was 320. I chose 284 (290 is so much closer to 284 than 320!) but the answer was 320.
I should have realized that my answer would have had to have been low. Since I rounded down, there was no way for my answer to be greater than the real answer, so 284 couldn't have been the correct answer. But it did get me, and since I'm at the beginning of my MCAT prep I thought this might be a "thing" that others have dealt with before. Apparently not. Good luck with your MCAT!
