Computer A takes 3 minutes to process an input while computer B takes 5 minutes. If computers A, B and C can process an average of 14 inputs in one hour, how many minutes does computer C alone take to process one input ?

Answer: Option B

Number of units processed by computer A in 1 minute
$$=\frac{1}{3}$$
Number of units processed by computer B in 1 minute
$$=\frac{1}{5}$$
Number of units processed by computer A, B and C in 1 minute
$$\begin{array}{rl}& =\frac{14\times 3}{60}\\ & \text{ = }\frac{7}{10}\end{array}$$
Number of units processed by computer C in 1 minute
$$\begin{array}{rl}& =\frac{7}{10}-\left(\frac{1}{3}+\frac{1}{5}\right)\\ & =\frac{7}{10}-\frac{8}{15}\\ & =\frac{5}{30}\\ & =\frac{1}{6}\end{array}$$
Hence, computer C takes 6 minutes to process one input alone.