The average of 2, 7, 6 and x is 5 and the average of 18, 1, 6, x and y is 10. What is the value of y?

Answer: Option C

We have:
$$\begin{array}{rl}& \Rightarrow \left(\frac{2+7+6+x}{5}\right)=5\\ & \Rightarrow 15+x=20\\ & \Rightarrow x=5\end{array}$$
Also,
$$\begin{array}{rl}& \Rightarrow \left(\frac{18+1+6+x+y}{5}\right)=10\\ & \Rightarrow 25+5+y=50\\ & \Rightarrow y=20\end{array}$$