QJEEM18Maf992: JEE Main 2018 Mathematics - Class 11 JEEM18Maf992 Solution: The number of four letter words that can be formed using the…

Case 1 :

When all the four letters different then no of words
= ⁵C₄ $$\times$$4!

Case 2 :

When out of four letters two letters are R and other two different letters are chosen from B, A, C, K then the no of words
= ⁴C₂ $$\times$$ $$\frac{4!}{2!}$$ = 72

Case 3 :

When out of four letters two letters are A and other two different letters are chosen from B, R, C, K then the no of words
= ⁴C₂ $$\times$$ $$\frac{4!}{2!}$$ = 72

Case 4 :

When word is formed using two R and two A then number of words
= $$\frac{4!}{2!2!}$$ = 6

So, total number of 4 letters words possible = 120 + 72 + 72 + 6 = 270