In how many different ways can the letters of the word SMART be arranged?

Answer: Option E

The given word contains 5 letters, all different.
∴ Required number of ways
$$\begin{array}{rl}& ={}^5{P}_5\\ & =5!\\ & =\left(5\times 4\times 3\times 2\times 1\right)\\ & =120\end{array}$$