Lesson: Introduction to GMAT Word Problems

Comment on Introduction to GMAT Word Problems

Please answer this one.

Before being simplified, the instructions for computing income tax in Country R were to add 2 percent of one’s annual income to the average (arithmetic mean) of 100 units of Country R’s currency and 1 percent of one’s annual income. Which of the following represents the simplified formula for computing the income tax, in Country R’s currency, for a person in that country whose annual income is i?

(A) 50 + i/200
(B) 50 + 3i/100
(C) 50 + i/40
(D) 100 + i/50
(E) 100 + 3i/100
gmat-admin's picture

Hey Brent, do you mind giving me a hand with a word-problem question?

Q: At a speed of 50 miles per hour, a certain car uses 1 gallon of gasoline every 30 miles. If the car starts with a full 12 gallon tank of gasoline and travels for 5 hours at 50 miles per hour, the amount of gasoline used would be what fraction of a full tank?

a) 3/25
b) 11/36
c) 7/12
d) 2/3
e) 25/36

Really appreciate it.
gmat-admin's picture

Thanks a lot and just want to say that you are always very helpful and awesome in your explanations! :)
gmat-admin's picture

Thanks brownpure!

I am not sure where this post should go, so apologies in advance.

I did a practice test and came across this question:

The points A, B, C and D are on a number line, not necessarily in that order. If the distance between A and B is 18 and the distance between C and D is 8, what is the distance between B and D?

(1) The distance between C and A is the same as the distance between C and B

(2) A is on the left of D on the number line

Here was my approach:

Statement (1)

C is the midpoint between A and B. Where both A and B lie we do not know:

---------A----------C------------B

Or

--------B-----------C------------A

From the information in the question stem, we know that the distance between A and B is 18. So, from (1) we know that the distance between B and C is 9 and from C to A is 9.
We are also told that the distance between C and D is 8

So, that could mean

-------A--D(?)---------C----------B

Or

------A---------------C------------D---B

We are not sure. If its closer to B, then the distance would be 9-8 = 1. If its further away and closer to A then the distance would be 9+8 = 17

So, (1) is insufficient.

(2)

--------A---D-----

Clearly, insufficient on it's own.

(1) and (2)

This tells us that:

-------------A----D----------C----------B

A being to the left of D

Or also

------------A-------------C------------D---B

To the left of A but much further away

So I concluded that both statements are insufficient and hence E. But the answer is C.

What have I missed?
gmat-admin's picture

Your solution is correct.
The answer is, indeed, E

See: https://gmatclub.com/forum/the-point-a-b-c-and-d-are-on-the-number-line-...

A general question regarding weighted avg in a word problem
https://gmatclub.com/forum/each-employee-of-a-certain-task-force-is-either-a-manager-or-a-directo-94413.html (from official GMAT practice exam 1)
In particular the 3rd post down by 'testluv' and the shortcut method which states ' The amount of skew is inversely proportional to the relative quantities of each item. If we have two groups, A, and B, then we have ("x" and "y" represent distance from the total average) eg. (# in A)/(# in B) = y/x
so in thise case y=manager, x = director (Given its inverse) 15,000 / 5000 = 3:1, which solves easily C.

Is this method covered in your videos? or can you confirm the logic/intuition behind this!
gmat-admin's picture

Question link: https://gmatclub.com/forum/each-employee-of-a-certain-task-force-is-eith...

This method is called alligation, and it basically works for 1 type of mixture question. Since the approach isn't very intuitive to most students, and since there are many cases in which it doesn't work, I've opted to stick with two other approaches (covered here https://www.gmatprepnow.com/module/gmat-word-problems/video/931 and here https://www.gmatprepnow.com/module/gmat-statistics/video/805)

I hope that helps.

Cheers,
Brent

Hi Brent,

Can you help me with this question?

There is at least one viper and at least one cobra in Pandora's box. How many cobras are there?

(1) From any two snakes from Pandora's box at least one is a viper.

(2) The total number of snakes in Pandora's box is 99.

The answer is A.

I couldn't get the explanation of it.

Have a nice day,
Nisa
gmat-admin's picture

Hi Brent,
Could you please help on this one ? Thank you

The investment banker's cash doubles every 30 minutes. If at 8.00am he had 60$ in his account, how much does he have at noon the same day ?
A.600.000, B. 60x2^6, C. 60x2^7, D. 60x2^4, E. 60x2^9
gmat-admin's picture

Let's make a table and look for a pattern.

TIME | MONEY
8:00 am: $60
8:30 am: ($60)(2) [since the $ doubles]
9:00 am: ($60)(2)(2)
9:30 am: ($60)(2)(2)(2)
10:00 am: ($60)(2)(2)(2)(2)
10:30 am: ($60)(2)(2)(2)(2)(2)
11:00 am: ($60)(2)(2)(2)(2)(2)(2)
11:30 am: ($60)(2)(2)(2)(2)(2)(2)(2)
12:00 pm: ($60)(2)(2)(2)(2)(2)(2)(2)(2) = 60 x 2^8

Cheers,
Brent

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