What is the value of (x - 1)(y + 1) ? (1) x + y = 4 (2) xy = 3

Question

What is the value of (x - 1)(y + 1) ?

(1) x + y = 4
(2) xy = 3

M36-130

PKN · Answer

Individually insufficient.

combining, we have two values of both x and y for which (x - 1)(y + 1) will have two values.

hence, insufficient.
Ans (E)

mygmat0101 · Answer

E

individual statements are insufficient.

we'll get two values of x and y 
x =1,3 y=3,1

so the binomial has 2 values

so E

Bunuel · Answer

Par of  GMAT CLUB'S New Year's Quantitative Challenge Set

Archit3110 · Answer

#1: x+y= 4

x,y can be (1,3) ( 2,2,) (4,0)

insufficient

#2 xy=3 
3,1 , 1/3*9 ... in sufficient

on combining we get (1,3 ) as the only number which would be sufficient .. IMO C

answer is C over E so because definite values of x & y are not sure and we get two value s in (x - 1)(y + 1) on substitution of (3,1) or (1,3)

Bunuel · Answer

Official Solution:

What is the value of  (x - 1)(y + 1)  ? 
 
(1)  x + y = 4 
 
The above equation has infinitely many solutions for  x  and  y . Not sufficient.
 
(2)  xy = 3 
 
The above equation has infinitely many solutions for  x  and  y . Not sufficient.
 
(1)+(2) From  x + y = 4  we can get that  x=1  and  y=3  or  x=3  and  y=1 . For the first case,  (x - 1)(y + 1)=0  but for the second case,  (x - 1)(y + 1)=6 . Not sufficient.

Answer: E

bumpbot · Answer

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What is the value of (x - 1)(y + 1) ? (1) x + y = 4 (2) xy = 3

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