DS

This topic has expert replies
Source: — Data Sufficiency |

User avatar
Legendary Member
Posts: 1460
Joined: Tue Dec 29, 2009 1:28 am
Thanked: 135 times
Followed by:7 members

by selango » Sat Jun 19, 2010 9:44 pm
x^2+y^2>100

rephrasing

(x+y)^2-2xy>100

from stmt1,

2xy<100

xy<50

xy can be of any value,so insufficient.

from stmt2,

(x+y)^2>200

The least value (>200) is x+y=14.2

what ever value of x and y,x^2+y^2>100

IMO B

Master | Next Rank: 500 Posts
Posts: 186
Joined: Fri May 28, 2010 1:05 am
Thanked: 11 times

by jube » Sun Jun 20, 2010 4:52 am
x^2 + y^2 = (x + y)^2 - 2xy

St 1 tells us only about 2xy so insuff.

St 2 tells us only about (x+y)^2 so again insuff.

St 1 & 2: tell us about the least value for the first term & greatest value for the 2nd term and hence are sufficient. Hence, C

Master | Next Rank: 500 Posts
Posts: 265
Joined: Mon Dec 28, 2009 9:45 pm
Thanked: 26 times
Followed by:2 members
GMAT Score:760

by mj78ind » Sun Jun 20, 2010 6:57 am
IMO B as well.

x+y > 10sqrt2

If x = y boundary condition, x = y > 5 sqrt2 for which x^2+y^2 always greater than 100.