Question

Q40. A boy has three library tickets and eight books of his interest in the library. Of these eight, he does not want to borrow Chemistry Part II unless Chemistry Part I is also borrowed. In how many ways can he choose the three books to be borrowed?

• A. (a) 56
• B. (b) 27
• C. (c) 36
• D. (d) 41

Answer 1

The correct option is D

(d) 41

The problem is a bit tricky. You must not think chem II must always be taken whenever chem I is taken. There are three sets of choices:

(i) Chem I but not chem II is chosen.

(ii) Chem I and chem II are both chosen.

(iii) Neither chem I nor chem II are chosen.

Number of choices corresponding to (i) through (iii)

(i) ⁶C₂ 15

(ii) 6

(iii) ⁶C₃ $\frac{6!}{3!3!}=\frac{4\times 5\times 6}{6}=20$