Which of the following is not equal to $\frac{18}{5}$ ?
(A) $\frac{6^{2}}{10}$
(B) $\frac{1}{5}[6(3)]$
(C) $\frac{18+1}{5+1}$
(D) 3.6
(E) $\sqrt{\frac{324}{25}}$
Evaluating each of the 5 choices,
(A) $\frac{6^{2}}{10}=\frac{36}{10}=\frac{18}{5}$
(B) $\frac{1}{5}[6(3)]=\frac{1}{5}[18]=\frac{18}{5}$
(C) $\frac{18+1}{5+1}=\frac{19}{6} \neq \frac{18}{5}$
(D) $3.6=\frac{36}{10}=\frac{18}{5}$
(E) $\sqrt{\frac{324}{25}}=\sqrt{\frac{18^{2}}{5^{2}}}=\frac{18}{5}$

Therefore, the only choice not equal to $\frac{18}{5}$ is (C).

ANSWER: (C)