2 PS Qs GMAT Prep (prob, at least)

oct07

please help to explain these 2 Qs. Thanks!

sujaysolanki · Posted: Mon Dec 03, 2007 9:21 am Post subject:

2.

At least one senior= total possibilities - no seniors in the selected members

= 10C3-6C3= 100

camitava · Posted: Mon Dec 03, 2007 11:52 am Post subject:

oct07, this problem appears to me somehow interesting... I will give a try to it. Now looking at the prob,
let ,
cost of the 15 homes = x1, x2, x3, x4 and so on.

Mean = (x1 + x2 + x3 + ... + x15) / 15 = 15 x 10^4
So (x1 + x2 + x3 + ... + x15) = 225 x 10^4

Median = should be the cost of 8th homes in increasing order of cost = 13 x 10^4.

Now I -> (165 - 130) x 10^3 = 35 x 10^3 - If interval is 5 x 10^3, then the last 15th building cost will be 165 x 10^3. But we are not sure the interval will be 5 x 10^3. - To me, its not always true.
Now III -> It should be always true because at least 7 houses should cost less than 13 x 10^4.
But as I can not be there and III should be, so IMO C.

Guest · Posted: Mon Dec 03, 2007 2:59 pm Post subject:

Thanks both of you!

Camitava:
The As is I. Please try again!

newmikeyork · Posted: Mon Dec 03, 2007 7:02 pm Post subject:

My answer -

I just did it intuitively. You could have 14 houses for 130 and one for a huge amount and still come to an average of 150, so II and III are not always true.

Obviously #I would hold in the case above, but let's take the other side and try to minimize the cost of the houses over 130. So to have a median of 130 we need at least 8 houses at 130 or under. Assuming all 8 were at 130 will minimize as much as possible the costs we need over 130 to get to the average.

8x130,000 = 1,040,000 (if any are less than 130, this number gets smaller)

So, if the total sum = 2,250,000 then the price of the 7 other houses has to equal that minus the price of the 8 at 130,000 = 1,210,000

1,210,000/7 = 172,857...

So each of the 7 must be over 165,000

camitava · Posted: Tue Dec 04, 2007 2:29 am Post subject:

What an explanation, newmikeyork! Thank u a lot. Now I think u I have got the problem... Wink