If 3b − |a| = 27, what is the value of b? (1) a^2 = 81 (2) a^3 0

Question

If 3b − |a| = 27, what is the value of b?

(1) a^2 = 81
(2) a^3 > 0

Kinshook · Answer

Asked: If 3b − |a| = 27, what is the value of b?

(1) a^2 = 81
|a| = 9
3b - 9 = 27
3b = 36
b = 12
SUFFICIENT

(2) a^3 > 0
|a| is unknown
3b - |a| = 27
3b = 27 + |a|
3b is unknown
b is unknown
NOT SUFFICIENT

IMO A

Pksri · Answer

Hi Kinshook,

I am bit confused in the first part. Why did you consider mod x as only +9 and not -9? Since x = +-9.

for, x^3 > 0, x must be positive.

Combining 1 & 2 we can say that x = 9 so we get the value of b.

Where am I making the mistake?

- Pradeep

Krishishere · Answer

Pradeep, condition 1 is sufficient even if you plug in both values of |a|.

xabi14 · Answer

Plugging in results in two values, while DS requires only one outcome as sufficient? CMIIW

Pradeep, condition 1 is sufficient even if you plug in both values of |a|.

If 3b − |a| = 27, what is the value of b? (1) a^2 = 81 (2) a^3 > 0