# Can you do well without doing any calculations?

Discussion in 'MCAT: Medical College Admissions Test' started by sexyman, Mar 15, 2007.

1. ### sexyman 5+ Year Member

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Apparently only 10% of the physical sciences involves calculations. I really suck at math without my calculator, and I frequently make mistakes and dont even realize it. Could I still get a 9-10 without doing any calculations by ignoring them until I'm done with the rest of the questions???

2. ### meds2008 Junior Member 5+ Year Member

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I read that 10% thing from TPR also but you have to remember that there will be variation from exam to exam especially when it comes to the number of calculations. Unless you think that you can get an incredible percentage of correct answers not involving calculations (which seems risky), just take the time to practice!

2 little pieces of advice: round off whenever you can (based on what your answer choices are) and work with fractions instead of decimals wherever possible (it usually simplifies calculations).

3. ### ocwaveoc Membership Revoked Removed

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Is this true that only about 10% (conservatively speaking say 20% max) require calculations in the physical science section? What the hell is on there then?? I'm really curious.

4. ### bigserve99 Member 10+ Year Member

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as I've practiced more and more, I agree that there is not too much actual calculations, perhaps as little as 10%. Most of the questions that involve an equation can be easily answered by simple manipulation of proportional vs. inversly proportional and constant variable relationships. Also, a multitude of the answer pool can be eliminated based on the degrees of magnitudes, positives vs. negatives, etc.

5. ### christian15213 Membership Revoked Removed

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Rounding works but be super careful... i.e. when doing division it is always a BIAAAA.... for example 15 / 10 hmmmm try this... move the 15 to 16 this is awsome because one you move the 15 up one your overall answer will be down (meaning lower... ) I always draw two arrows to keep track... Moreover the bottom / denomenator is totally different it stays in the same direction... if we would have moved the 10 to 9 then the answer would have been lower that that as well. YOU ShOULD try and avoid overlapping when doing this trick... meaning moving the bottom up and the top up... this produces a conflicting result of what to choose, up or down, sometimes....

Back to our example when we took the 15 up to 16... we can now factor out by saying 8/5 which is roughly 1.6 (well I shouldn't say roughly) and we know our answer is lowering that that = 1.5 But lets say we didn't know our math rules i.e. anything divided into 5 is by .2 so 9 into 5 is one plus the 4 x .2 which is 1.8... 1/4 = .25 so 9 / 4 = 2 plus .25 = 2.25...

If we took 8 which our overall at this point is lower and then took the 5 and raised it to 6 our overall would be confused... 8=4 and 6 would equal 3... 4 / 3 = 1.3333 and we really didn't have a clear picture of where to go, lower or higher... So again, try to keep things in the same direction... if I took the 5 down to 4 and thus made 8/2 = 4 and 4/2 = 2 the answer would be two... this is still a better result than 1.3333 because we know our answer should be lower than the obtained result...

Another awsome math technique... !!!!!

*****Dividing decimals... ok, .6/.3 = 2 yea... why? 1-1=0<<<you;ll see in a minute...

.8/.02 = 8/2 = 4/1 = 4 Now take the 4 and minus 1 <<<<SO LARS left add right subtract... works here too... <<<<<< But where did we get -1 from? .8 = 8 when we moved it over to the 8 once (1) .02 became 2 when we moved the decimal to the whole number side twice (2)... 1-2 = -1... Oh this method so works... the answer is 40 because we had to move to the right once because according to LARS we have a - or 1subtract the answer would be 4 0

Now, that is when the bigger / larger number is on the top... If the reverse is true = smaller number on Numerator... then this is how it goes... i.e. .02 / .8 so what do we have... 2 or easier to make it 20 / 8 = 5 / 2 which would be 2.5 but remember we moved the .02 to 20 which is 1;2;3 places to the whole number... subtract that from the placed we moved of the denominator and we get 3-1 (1 comes from the .8 getting moved one place to point 8) so the answer is two positive so now we must go to the LEFT ADD... so going to the left I can take the 2.5 and move it two places to the left to .025

Enough with that...

Square roots... I love doing squares in my head now... I have to admit EK was awsome on this front...

anynumber you get just recognize the natural square around it... the square root of 50 has to be between the square of 49 = 7 * 7 and 56 = 8 * 8... so because the number is so close to 49 I know my number has to be close by it... and I would guess it is something like 7.1 and the answer is... 7.07... That is a damn good approximation...

now for exponents there are tricks for that too... but I am tired... Hope this extremly helped...

6. ### christian15213 Membership Revoked Removed

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If you wanted exponent help let me know... I can help you...

7. ### estairella Senior Member 10+ Year Member

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0.8/0.02 is equivalent to 80/2. Half of 80 is 40.

0.02/0.8 is slightly bigger than 0.02 (because 0.8 is slightly smaller than 1).

Estimations and quick calculations are useful because they're quick. I can't tell if it's just your explanation, but the system you suggested is not quick.

8. ### christian15213 Membership Revoked Removed

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Yes, but there is a lot of estimations assuming .8 / 0.02 is equivilant 80/2 where would one think that from now where? I know my method seems like it takes time really and truly it takes a matter of seconds to work out... In fact one could do it in there on head... to me the estimation and getting numbers to be divisiable by the denominator makes almost any of this math super easy... the exponent rules and what have you are good just as well.

Enough practice and you will be thinking of why you ever used a calculator. Not really but you know what I mean.

9. ### DrBowtie Final Countdown Moderator Emeritus 10+ Year Member

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Estimation is overrated. The numbers aren't close enough that a very rough estimation won't work. Often times if you can get the right order of magnitude, you'll get the right answer.

10. ### christian15213 Membership Revoked Removed

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I agree with you but think about it...

If I say to you divide .01 / .1... with just estimating that and trying to blindly choose an answer is dangerous...

10
1
.1
.01
100

And for someone panicking wondering to themselves... OMG what do I do with that.

bam 2-1 = 1 now I know 1/1 =1 and move it back to the left once .1 is my answer...

that doesn't take much time...

11. ### estairella Senior Member 10+ Year Member

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I wouldn't trust a doctor who can't divide anything by 0.1 in their heads with my patient charts....

12. ### ocwaveoc Membership Revoked Removed

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I thought that your tips were very helpful. I try to work the problems the way you've done it and by rough estimates as well. I can see that with a little bit of practice, your method can yield answers very rapidly.

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