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

A. 840

B. 1680

C. 2520

D. 5040

E. None of these

Answer: Option A

Solution(By Examveda Team)

The given word contains 7 letters of which D is taken 3 times.
∴ Required number of ways
$$\eqalign{ & = \frac{{7!}}{{3!}} \cr & = \frac{{7 \times 6 \times 5 \times 4 \times 3!}}{{3!}} \cr & = \left( {7 \times 6 \times 5 \times 4} \right) \cr & = 840 \cr} $$