21.A student has to answer 10 questions, choosing at least 4 fromeach of part A and B. If there are 6 questions in part A and 7 inpart B. In how many ways can the student choose 10 questions?

Explanation

Total no. of questions in part `A =6`

Total no. of questions in part B `=7`

Total no. of ways can the student choose `10` questions

`=>6_(C_4)**7_(C_6)+6_(C_5)**5_(C_5)+6_(C_6)**7_(C_4)`

`=>15**7+6**21+1**35`

`=>266`