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