Does x = 15? (1) The average of x, y, and z is 5. (2) y = -z

Question

Does x = 15?

(1) The average of x, y, and z is 5.

(2) y = -z

Hatakekakashi · Answer

(1) x+y+z = 15

x can be 15 but we don't know that yet

(2) insufficient, provides no data about X

combining we know that y+z = 0

x= 15

(C) imo

varun4s · Answer

Statement 1:    \frac{x+y+z}{3} = 5

x+y+z= 15 . No inf about x, y and z

Statement 2:   y=-z

So y+z=0

Put (2) in (1)
 
x+y=z= 15
x+0= 15
x= 15

Answer: C.

DavidTutorexamPAL · Answer

Let's try using numbers, an Alternative approach.

(1) If x = 15 and y=z=0 then statement (1) holds and x=15. However, If x=y=z=5 statement (1) holds and x=5.
Insufficient.

(2) Ok... but what is the value of x?
Insufficient.

Combined:
Let's say x=15. Then y=z=0 and both statements (1) and (2) hold.
Let's try making x different from 15. Say x = 10. Then y+z=15-10=5. But y = -z so y+z = 0! This is impossible.
Trying another number, say x = 5, we will get y+z=15-5=10, which is also impossible.
In fact, because y+z=0 than only x=15 can work.
Sufficient.

(C) is our answer.

rishabhmishra · Answer

IMO C 
as we can say from first statement x+y+z= 15 it means x=15 y=0,z=0 or X=5,y=5,z=5 so we can't say anything insufficient.
second statement y=-z doesn't tell anything about x and combining both we get to know that y and z will be cancelled only x=15.

Does x = 15? (1) The average of x, y, and z is 5. (2) y = -z

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GMAT Data Sufficiency (DS) Questions

Does x = 15? (1) The average of x, y, and z is 5. (2) y = -z

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