Grade 11Discuss with colleagues and IITians
10 different letters of alphabet are given words with 4 letters are formed from these letters then the number of words which have at least one letter repeated is. AnswerSuppose we have one letter repeated Then total ways to select are 10C3 and arranging them are 3! Total ways=10C3×3!Now let 2 letters repeat then the total ways of selection are 10C2. and the ways of arranging them are 2! Total ways=10C2×2! total number of words formed are10C3×3!+10C2×2!
