WAEC - Further Mathematics (2008 - No. 31)
A test consists of 12 questions out of which candidates are to answer 10. If the first 6 are compulsory, in how many ways can each candidate select her questions?
40
25
15
10
คำอธิบาย
The first 6 questions can only be selected in 1 way.
The remaining 4 questions can be selected in \(^{6}C_{4}\) ways.
= \(\frac{6!}{(6 - 4)! 4!} = 15\)