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sud21: Master | Next Rank: 500 Posts; Posts: 344; Joined: Sat Nov 12, 2011 3:21 am; Thanked: 1 times; Followed by:2 members

word problem

by sud21 » Thu Jan 19, 2012 11:17 pm

There are some green balls and blue balls in a box. what is the total number of the balls?
1) The number of the green balls is 1/3 of the number of the total balls
2) If one green ball is taken out, the remaining green balls are 1/5 of the balls in the box.

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Source: Beat The GMAT — Quantitative Reasoning | Thu Jan 19, 2012 11:17 pm

sam2304: Legendary Member; Posts: 1239; Joined: Tue Apr 26, 2011 6:25 am; Thanked: 233 times; Followed by:26 members; GMAT Score:680

by sam2304 » Fri Jan 20, 2012 5:16 am

There are some green balls and blue balls in a box. what is the total number of the balls?
1) The number of the green balls is 1/3 of the number of the total balls
2) If one green ball is taken out, the remaining green balls are 1/5 of the balls in the box.

1.No info about total balls. All we know is the ratio. INSUFF.
2.No info about blue balls/total balls. INSUFF.

Combining 1 & 2, we can get no of green balls with 2 and with both we can get the total balls.

IMO C.

Getting defeated is just a temporary notion, giving it up is what makes it permanent.
https://gmatandbeyond.blogspot.in/

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pm; Location: Vancouver, BC; Thanked: 5254 times; Followed by:1268 members; GMAT Score:770

by Brent@GMATPrepNow » Fri Jan 20, 2012 6:12 am

sud21 wrote:There are some green balls and blue balls in a box. what is the total number of the balls?
1) The number of the green balls is 1/3 of the number of the total balls
2) If one green ball is taken out, the remaining green balls are 1/5 of the balls in the box.

Let G = # of green balls
Let B = # of blue balls

Rewrite target question as "What is the value of G + B?"

Statement 1:
G = (1/3)(G+B)
To simplify, multiple both sides by 3 to get: 3G = B+G
Simplify to get: 2G-B = 0
Since we cannot find the value of G+B, statement 1 is NOT SUFFICIENT

Statement 2:
G-1 = (1/5)(G-1+B)
To simplify, multiple both sides by 5 to get: 5G-5 = G-1+B
Simplify to get: 4G-B = 4
Since we cannot find the value of G+B, statement 2 is NOT SUFFICIENT

Statements 1 & 2:
We now have two equations (2G-B = 0 and 4G-B = 4), which we could solve for G and B
As such, we now have SUFFICIENT information to find the value of G+B

Answer = C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com