Lesson: Assigning Variables

Comment on Assigning Variables

Hi Brent, Your explanations are awsome!
i would like to ask you :
How are we (non americans are supposed to deal with the nickel / quarter thing (Talking about the first ressource above) is there any trick i could learn so i can deal with this issue ?
gmat-admin's picture

Great question, Ben!
The first linked question in the Related Resources box is not an official GMAT question. I seriously doubt that an official question would require test-takers to know the value of dimes, nickels, etc. Instead, they will just say $0.10, $0.05, etc

BTW, I'm not American either :-)

Thank you !
This would be a real struggle for intational students. I just walked through the OG, not a single one looks like that.
Thank you again, your videos are the best ressources i've seen so far !
Have a good day

Brent this might seem dumb or maybe I just am tired today but why is your 'twice as many cats as dogs': 2D = 1C?

Shouldn't it be 2C = 1D? For every 2 cats there's one dog?
gmat-admin's picture

You're not alone; many students mistakenly believe that "twice as many cats as dogs" translates into 2C = 1D.

If there are twice as many cats as dogs, then we can say that (the number of cats) ≠ (the number of dogs)

Our goal is to create an equation that we can solve. So, how do we make the above quantities equal?

Do we take the larger quantity (the number of cats) and make it even bigger my multiplying that quantity by 2? Definitely not.

Instead, we take the smaller value (the number of dog) and multiply it by 2 to get: C = 2D.

We can also try this with some specific values.

If there are "twice as many cats as dogs," then it's possible that there are 10 cats and 5 dogs. At this point, it's clear that (the number of cats) ≠ (the number of dogs), because when we replace the bracketed parts with 10 and 5, we get: 10 ≠ 5

How do we make the two quantities equal? We take the smaller quantity, 5 (which represents the number of dogs) and multiply it by 2 to get: 10 = (2)(5)

So, we can also write: (the number of cats) = 2(the number of dogs)

Hi Brent, In the 3rd Reinforcement question (the question on ropes), would the answer be D if we were to mention in the question that all the ropes have integer lengths? Thanks!
gmat-admin's picture

Question link: https://gmatclub.com/forum/a-length-of-rope-is-cut-into-three-different-...

That's right, Bullzi. If the 3 ropes had to have integer lengths, then the correct answer would be D

Hi, Brent! This might be a silly question. But I had trouble with this several times.
N=2009 population;
1.1N=2010 population.

Why not
gmat-admin's picture

Your calculations are very close to mine, except you missed something.

If we want to algebraically represent a number that's 10% greater than N, then we can go about it in two ways:

#1) 1.1N

#2 N + (10% of N) = N + 0.1N
= 1N + 0.1N
= 1.1N

Does that help?

For odd consecutive numbers wouldn't the answer be 2a +1, 2a+3, 2a+5, 2a+7?
gmat-admin's picture

That approach will also work. However, once you solve for the variable a (e.g., a = 7), you must remember to plug that a-value into your predefined expressions to get the actual answer (e.g., 2a + 1 = 2(7) + 1 = 15)

That said, I find it easier to let x = the smallest odd integer, x + 2 the next odd integer, x + 4 the next, and so on.

Hi Brent!

I've noticed in a couple of questions there is no reference to the value of dimes/quarters/nickels etc. Is this something that we have to keep in mind before the exam or will it be given in the question?
gmat-admin's picture

Great question, Swatato.

The GMAT does not require you to know the values of dimes, quarters or nickels.
IF the test-makers were to use any of those terms, they would be certain to tell you the value of each coin.


Q link: https://gmatclub.com/forum/ana-is-a-girl-and-has-the-same-number-of-brothers-as-sisters-andrew-221484.html

I answered this question logically but consumed time, is there any tricks to solve this faster? Thanks!
gmat-admin's picture

Question link: https://gmatclub.com/forum/ana-is-a-girl-and-has-the-same-number-of-brot...

Karishma shows that we can apply some logic to the question here: https://gmatclub.com/forum/ana-is-a-girl-and-has-the-same-number-of-brot...

Alternatively, in my solution (https://gmatclub.com/forum/ana-is-a-girl-and-has-the-same-number-of-brot...), I'm able to quickly write the following system of equations:
B = G - 1
2B - 2 = G

From here, it shouldn't take long to solve the system for B and G.



what if I assign Alice to x, I got answer choice C eventually, can you point out what I'm doing wrong?

I think 3x = 12 + x, x = 6, so Betty must be 12 years old
gmat-admin's picture

Question link: https://gmatclub.com/forum/carol-is-three-times-alice-s-age-but-only-twi...

If x = Alice's age, then...
3x = Carol's age (since Carol is three times Alice’s age)
And 1.5x = Betty's age (since Carol is twice as old as Betty, we can also say that Betty's age is half that of Carol)

From here we can use the information that says "Alice is twelve years younger than Carol. How old is Betty?"
This means: (Alice's age) = (Carol's age) - 12
Substitute to get: x = 3x - 12
Solve to get x = 6

This means Alice is 6 years old, Carol is 18 years old, and Betty is 9 years old.

I had to say that word questions are real tricky in term of wordings and the answer, I should be extremely careful
gmat-admin's picture

Indeed! Many students find this to be the most difficult topic on the GMAT.

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