two hard ps questions

This topic has expert replies
Junior | Next Rank: 30 Posts
Posts: 17
Joined: 02 Jun 2008

two hard ps questions

by yakiraz » Fri Jun 27, 2008 9:07 am
A) In a certain restaurant there are 4 different dressing. a customer can choose 0,1,2 or 3 different dressing. How many different dressing can a customer choose?

B) A, B, C, and X are prime consecutive positive numbers. what is A+B+C in terms of X.
1)4X+6
2)3X+12
3)3X+5
4)X^2
5)X

please expalin how you got to the answer :lol:

Master | Next Rank: 500 Posts
Posts: 132
Joined: 27 Apr 2008
Location: Portugal
Thanked: 7 times

by atlantic » Fri Jun 27, 2008 9:15 am
Hi Yakiraz,

A) You can chose 0, 1, 2 or 3 diferent dressings.

If you choose 0, you have only 1 way to dress the meal

If you choose 1, you have 4 ways (or 4C1).

If you choose 2, you have (4C2)

If you choose 3, you have (4C3)

So 1+4+6+4 = 15

OA?

User avatar
Master | Next Rank: 500 Posts
Posts: 200
Joined: 17 Jun 2007
Location: Canada
Thanked: 9 times

Re: two hard ps questions

by beeparoo » Fri Jun 27, 2008 9:22 am
yakiraz wrote:A, B, C, and X are prime consecutive positive numbers. what is A+B+C in terms of X.
1)4X+6
2)3X+12
3)3X+5
4)X^2
5)X

please expalin how you got to the answer :lol:
Just by looking at the answer choices, I can't help but feel there is some vital information missing from the question stem.
Where did you get this question?

Master | Next Rank: 500 Posts
Posts: 132
Joined: 27 Apr 2008
Location: Portugal
Thanked: 7 times

by atlantic » Fri Jun 27, 2008 9:41 am
Sure beeparoo, in B setence is incomplete. Waiting for more information

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2615
Joined: 02 Jun 2008
Location: Toronto
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

Re: two hard ps questions

by Ian Stewart » Fri Jun 27, 2008 10:33 am
yakiraz wrote:A) In a certain restaurant there are 4 different dressing. a customer can choose 0,1,2 or 3 different dressing. How many different dressing can a customer choose?
atlantic definitely has this right, above, and it's worthwhile understanding that method. You can also look at it this way: for each dressing, the customer has 2 choices: use it, or don't. So with no restrictions, the customer has 2^4 = 16 choices of dressing combinations. If he chooses 0, 1, 2 or 3 different dressings, he did not choose 4 different dressings, and there's only one way to choose all four dressings: say yes to everything. Thus there are 16 - 1 = 15 ways to choose 0, 1, 2 or 3.
yakiraz wrote: B) A, B, C, and X are prime consecutive positive numbers. what is A+B+C in terms of X.
1)4X+6
2)3X+12
3)3X+5
4)X^2
5)X
There are no equation-based formulas whatsoever in mathematics that relate any string of primes by addition. Indeed, there are many famous unsolved problems in math about the addition of primes: Goldbach's conjecture, for example. There is no way this question can contain the word 'prime'. My best guess is that the question means to talk about 'odd' numbers, not 'prime' numbers, and that the second answer choice is supposed to have a minus sign, not a plus sign. But that's just a guess. What's the source?
If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Junior | Next Rank: 30 Posts
Posts: 14
Joined: 02 Jun 2008
Thanked: 3 times

by llewellyn27 » Sat Jun 28, 2008 3:39 pm
atlantic

Im really confised with this 4C2 etc.

can you please explain further