JEE Main 2021 (Online) 3rd August Evening ShiftQuestion 1
If six letter words (with or without meaning) are formed using $A,B,C,D,E$ and $F$, then the number of words, in which exactly one of these alphabets is repeated three times and the other three are distinct, is $\_\_\_\_\_\_$ .
Permutation and Combination
Answer$7200$
Solution
Choose the tripled letter: 6; place its 3 positions: $\binom63=20$; choose and arrange 3 distinct others from 5: ${}^5P_3=60$. Total $=6\cdot20\cdot60=7200$.