Q. 8 B4.3( 6 Votes )
How many different selections of 4 books can be made from 10 different books, if
two particular books are always selected
Answer :
It is told that two books are always selected.
It is similar to selecting 2 books out of the remaining 8 books as 2 books are already selected.
Let us assume the choosing the no. of ways be N1,
⇒ N1 = choosing 2 books out of 8 books
⇒ N1 = 8C2
We know that 
And also n! = (n)(n – 1)(n – 2)…………2.1
⇒ 
⇒ 
⇒ 
⇒ N1 = 28 ways
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