x, y, and z are consecutive integers, and x < y < z.

[M7MBA]

x, y, and z are consecutive integers, and x < y < z. What is the average of x, y, and z?

(1) x = 11

(2) The average of y and z is 12.5.

The OA is the option _D_

Source: Manhattan GMAT

[swerve]

1. Clearly sufficient.

2. Take 3 numbers

\(a-d\, a\, a+d\)

avg \(=\frac{ a-d + a + a+d}{3} = \frac{3a}{3} = a\)

Hence we need to know \(a\) only... \(d\) is 1

now \(\frac{y+z}{2} = \frac{25}{2}\)

\(a+a+d = 25\)
\(2a+1 = 25\)
\(a =\frac{24}{2} \Rightarrow 12 \)

Hence sufficient.

So the answer is __D__