## mathmath333 one year ago There are 7 different books in a library. A girl can borrow book B if only book A is borrowed. In how many ways can she borrow 3 books ?

1. mathmath333

\large \color{black}{\begin{align} & \normalsize \text{There are 7 different books in a library. }\hspace{.33em}\\~\\ & \normalsize \text{A girl can borrow book B if only book A is borrowed.} \hspace{.33em}\\~\\ & \normalsize \text{In how many ways can she borrow 3 books ?} \hspace{.33em}\\~\\ & a.)\ 15 \hspace{.33em}\\~\\ & b.)\ 20 \hspace{.33em}\\~\\ & c.)\ 25 \hspace{.33em}\\~\\ & d.)\ 30 \hspace{.33em}\\~\\ \end{align}}

2. anonymous

is there any specific arrange for A and B ?

3. mathmate

 A girl can borrow book B if only book A is borrowed  Must book A be borrowed by the girl or by someone else?

4. phi

25

5. mathmath333

book B can be borrowed only if book A is borrowed

6. mathmath333

yes 25 is answer given , how u got it

7. zzr0ck3r

I am confused by the question. But phi is not :)

8. mathmath333

"A girl can borrow book B if only book A is borrowed" i think "Must book A be borrowed by the girl "

9. mathmath333

lol m also confused by thhe question

10. mathmate

"A girl can borrow book B if only she also borrows book A" is the intended wording if 25 is the final answer.

11. phi

First, order does not matter. I broke the problem into two parts. say one of the 3 books we choose is A. then we have a choice of 6C2 for the other two. that is 15 combinations say we did not choose A. then that means we can not choose B either. that leaves 5 books from which to choose 3 5C3= 10 more combinations 15+10= 25

12. mathmath333

"A girl can borrow book B if only she also borrows book A" is the intended wording if 25 is the final answer. yea i think so ,

13. mathmath333

thnx