NBME 22 2.4 (NBME Answers)

Retired NBME 22 Answers

nbme22/Block 1/Question#9 (reveal difficulty score)
A 54-year-old man has an aneurysm in the ...
2.4 🔍 / 📺 / 🌳 / 📖
tags: calculation

+17 upvote downvote
submitted by ∗keycompany(351)

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Flow Rate = Velocity x Cross-Sectional Area

2 cm^2 x 20 cm/sec x 60 sec/min x 1 L/1,000 cm^3 = 2.4 L/min

1,000 cm^3 = 1 L

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seagull Well, I missed this one. I don't even feel bad. +78

link981 @keycompany a small typo, 100 cm^3 = 1 L not 1000cm^3. 1000 mL^3= 1 L +1

hello @keycompany how did you edit your original comment to fix your typo? +1

winelover777 Pretty sure @keycompany was correct. 1 L = 1000 cm^3. Otherwise the answer would be 24. +4

drdoom 1 centimeter is a distance. (A line.) +1

drdoom If we multiply a line by another line, we get a surface area. (A piece of paper.) +1

drdoom If we multiply the piece of paper by another line, we get volume. (A cube. A box.) +1

drdoom If we fill the box with a fluid, we will have 1 mL of this fluid. +1

drdoom If we have a thousand of these boxes, we have 1 L of fluid. +1

drdoom 1,ooo mL = 1 Liter = 1,ooo centimeter³ +1

if one still doesn't understand to add on .. 1000 cm^3 = 1000 ml 1000ml = 1 Litre

+5/- ribosome01(-3)

+6 upvote downvote
submitted by ∗nwinkelmann(366)

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I've never been good at converting units :( lol so had to ask my brother. He told me that:

distance × distance = distance² = area

and,

distance × distance × distance = distance² × distance = distance³ = volume

Gotta love public school for never been taught that ... geesh (obviously I've done the equations and stuff, just never been told it that way/that simple before). Knowing that makes figuring out the equation much easier:

Flow rate = velocity × CSA = 20 cm/sec × 2cm² = 40cm³/sec

To convert to L/min, just multiply:

40cm³/sec × 60 sec/min × 1L/1,000cm³ = 2400 L/1,000 min = 2.4 L/min

Hope this helped!

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impostersyndromel1000 to all my public school peeps out there (and not the nice public schools in rich areas, the real public schools)... we made it! +4

angelaq11 Thankfully I was taught how to convert units, but let me tell you that I was SO lost on this one. It's USELESS to know how to do it if you (I, I mean I) don't know the damn formula xD. Obviously got this one wrong, but it's good to know that if it ever comes up again (and I know it won't) I already know it. +2

This is all you need for conversions:

1cm3 = 1 ml ... thus 40 cm3 = 40 ml

So to make it faster I would do it like this

40 ml/sec * 60 sec/1min * 1L/1000ml = 2.4 L/min

+3/- majoav1(2)

+2 upvote downvote
submitted by seracen(15)

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Ugh, sorry, getting used to the formatting, and accidentally posted it in the wrong place.

Anyways, to reiterate, I always just look at the units. It wants L/min, I'm given cm^2 and cm/sec

So I multiply, to get volume out of it (cm^3), then convert seconds to minutes.

Thus, it's basically 2x2x6, in some shape or form after placing the decimals appropriately. Good thing they didn't add that particular wrinkle, I'll take my remedial math skills and bug out, haha...

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submitted by googaga(2)

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Testing testing 123. This is a test post to see if things un scram ble by typing a comment. Thanks.

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drdoom i respect this attempt but i don't think it works that way +2

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submitted by ∗usmleboy(19)

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This question was on my MCAT and I laughed when I saw it.

Things you gave to know: cm^3 = mL , then how to convert units.

2cm^2 x 20 cm/sec = 40cm^3 / sec = 40 mL / sec

From here just convert 40 mL / sec to L / min

40 mL / sec x 1 L / 1000 mL x 60 sec / 1 minute = 2.4 L / min

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-1 upvote downvote
submitted by ∗kernicterusthefrog(139)

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Just in case that lovely little equation provided by @keycompany wasn't quite enough for you, here's a link to a more complete explanation by Kahn Academy. Helped me, when I looked at the equation and said, whaaaa?

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If, like me, you dislike memorizing formulas, but are okay doing the actual math, I always just look at the units. It wanted L/min, and I had to get it using cm^2 and cm/sec...

Well, I know cm^3 gives volume (L) after bashing out a few conversions, so multiply it is!

Then I know to turn seconds into minutes, so multiply by 60.

Now, at this point, I knew my decimals were off, but still, 4x6 = 24, so it's some version of that. Had they included 24 or .24 as answers, I'd have actually had to pay attention to my conversions.

Anyways, I hope that helps!

+4/- seracen(15)

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