science books

Expert replies

uptowngirl92: Master | Next Rank: 500 Posts; Posts: 447; Joined: Sun Apr 19, 2009 9:08 pm; Location: Kolkata,India; Thanked: 7 times; GMAT Score:670

by uptowngirl92 » Sat Jun 06, 2009 4:10 am

Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics. 50 are on geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?
(A) 81
(B) 159
(C) 166
(D) 285
(E) 324

[spoiler]OA:E[/spoiler]

help guys!Detailed explanation needed!

Like this post

Source: Beat The GMAT — Problem Solving | Sat Jun 06, 2009 4:10 am

DanaJ: Site Admin; Posts: 2567; Joined: Thu Jan 01, 2009 10:05 amFollowed by: 550 members; Thanked: 712 times; GMAT Score:770

by DanaJ » Sat Jun 06, 2009 5:56 am

This is a worst case scenario question.

Consider you're the unluckiest person in the world: then when you take some books out of the library, it just so happens that they're all from the sets that DON'T have at least 80 books, which means that you take out 50 + 50 + 65 = 165 books with no success. Then you start on the other two sets. You might think that taking an extra 80 books out will suffice, but what if you take 40 out of the physics books and 40 out of the chemistry books? To be 100% sure you've taken at least 80 books from one subject, you need to take out another 80 + 79 = 159 books. This way, you're absolutely sure you've gotten the required quota out of there.

Take less than 159 books out of there, and you might be carrying 79 books of one subject and 79 books of the other. But take the 159 and you're 100% sure you've taken at least 80 books of the same subject.

The grand total will be 165 + 159 = 324.

Like this post

uptowngirl92: Master | Next Rank: 500 Posts; Posts: 447; Joined: Sun Apr 19, 2009 9:08 pm; Location: Kolkata,India; Thanked: 7 times; GMAT Score:670

by uptowngirl92 » Wed Jun 10, 2009 9:33 pm

DanaJ wrote:. Then you start on the other two sets. You might think that taking an extra 80 books out will suffice, but what if you take 40 out of the physics books and 40 out of the chemistry books? To be 100% sure you've taken at least 80 books from one subject, you need to take out another 80 + 79 = 159 books. This way, you're absolutely sure you've gotten the required quota out of there.

Take less than 159 books out of there, and you might be carrying 79 books of one subject and 79 books of the other. But take the 159 and you're 100% sure you've taken at least 80 books of the same subject.

The grand total will be 165 + 159 = 324.

I did'nt understand the last part.Where did the 79 come from??

Like this post

tohellandback: Legendary Member; Posts: 752; Joined: Sun May 17, 2009 11:04 pm; Location: Tokyo; Thanked: 81 times; GMAT Score:680

by tohellandback » Thu Jun 11, 2009 12:53 am

This is more of a reasoning question than maths..
we want to know how many books MUST be removed to ensure that 80 of the books removed are on the same science. so we have to take the worst case.
Now botany,zoology and geology books are less than 80 in number. we are looking for worst case, so let's say we are running a bad luck and we get them first
.so 50+50+50
now lets say we got 79 physics books and our luck is so bad that we don't get the 80th one(worst case,remember?). thats why we add 79 here. same for the chemistry books
after this whatever book we get, it will complete 80 books of the same color condition
so 1 here
total=50+50+65+79+79+1
hope i helped

The powers of two are bloody impolite!!

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review