Expert: Robi Bhattacharjee - 9/17/2008

Question
QUESTION: 1)(LOGIC) At a party there are 2 more men than women. If 4 men were to leave and 2 women were to arrive, there would be twice as many women as men. How many guests are at the party?

2)(IMPLICATION) I have 4 blue eggs and 1 green egg. Given that robins lay blue eggs, all green eggs are laid by parrots and hens' egg contain salmonella, which one can be deduced? (the answer to q2 is (C) ),
(A) Robins outnumber parrots
(B) None of my eggs contains salmonella
(C) One of my eggs is from a parrot
(D) Hens are bigger than robins

I'm not sure how I'm supposed to work out both questions. Thank you for your help!

ANSWER: Hello Selina,

Good questions!

For the first question, the best way to do it is to set up equations. Let m be the number of men, and w be the number of women.

So m = w + 2, this is because there are two more men than women.

Also, (m-4)*2 = (w+2), this is because if 4 men left and 2 women came, there would be twice as many men as women.

now m = w + 2

and 2m - 8 = w + 2  I got these by simplifying the above equations.

now, if we simplify the second equation further, we get 2m - w = 10.

now m = w + 2 since that is one of our equations, so we can plug it in and we get 2(w + 2) - w = 10

so 2w + 4 - w = 10

so w + 4 = 10

so w = 6 which means m = w+2 = 6 + 2 = 8.

So there are 6 + 8 = 14 people at the party.

For the second question, you have four blue eggs which have to be laid by Robins, and one green egg that has to be laid by a parrot since parrots lay green eggs. So that means the answer is c one of your eggs if from a parrot.


I hope this helped,

Robi

---------- FOLLOW-UP ----------

QUESTION: Hi, thank you very much for your help! I'm still a little uncertain about q2 though. Why can't the answer be A or B?

Answer
Hi Selina,

On question two, it is asking what you know for certain, not what might be true. This means that the answer cannot be that there are more Robins than parrots since there may only be four Robin eggs in the worlds and you have all of them while there are hundreds of parrot eggs. You also cannot assume your eggs are devoid of salmonella since it says that all chicken eggs have salmonella but it doesn't say that Robin/Parrot eggs do not have salmonella, so they could have it for all you know.






I hope this helped,

Robi