Not every difficult MCAT question is inherently tough. You may find yourself faced with a potentially easy physics or chemistry MCAT question, only made tough by the detailed and tedious math required.
This is especially true when fractions are involved, in the form of dimensional analysis, ratios, proportions, or finding percent values. The math is certainly doable using pen and paper, but is it worth the time wasted?
The video below shows you how to quickly tackle fractions, ratios, percentages and proportions on MCAT style questions without a calculator.
MCAT Fractions, Ratios, Percentages, and Proportions
(click here to watch on YouTube or catch the video transcript here)
MCAT Questions Solved In This Video:
Molarity Question: Find the molarity of a solution made by dissolving 35g of NaBr in 500 ml of water
Hybridization Question: Find the percent ‘d’’ character in a molecule that has sp3d hybridization
Gravitational Force Question: What is the gravitational force on a planet if the mass is 3 times the mass of earth but its radius is only 2 times the radius of the earth?
This is video 5 in my series on MCAT Math Without A Calculator. Click HERE for the entire series
Leah, how do I do something like this in my head?
(27.4 mL)(0.0154 M) = (20 mL)(x)
I can’t seem to figure out how to take (0.01) of 30 (rounded). Or any other value like 0.2, 0.1, 0.01, etc
Hi Leah,
Thanks so much for your videos – they are super helpful! For your above video – I am a little confused with the gravitational force question – specifically with how you would take into account the r^2 when solving for F. Wouldn’t you only multiply the radius by 1.4? Can you clarify how to treat exponents when doing ratios/relationships in equations? One example I was given was an equation where you have some variable on the top of the equation, and one on the bottom – say it is r^4 – when thinking about proportionality in equations, if you increase the variable on the top, you can’t simply decrease the r^4 on the bottom by the same factor, because of the ^4 – so you would have to take the square of the square of that number to get the appropriate factor to multiply (or divide) by. Sorry if this is confusing, but I’m a little confused with how you did it in your video!
hi, wonderful stuff.
you solved the fraction ” 7/33 ” , by making ” 33 ” into a hundred by multiplying ” 33 with 3 “. okay.
But what if I’m asked a question, ” 7/44 “. How do I make the ” 44 ” to a hundred.
Regards.
I’d find another way to round. 7/44 is close to 7/42 which is 1/6