Advertisements
Advertisements
प्रश्न
Find n, if `""^"n""C"_("n" - 2)` = 15
उत्तर
`""^"n""C"_("n" - 2)` = 15
∴ `("n"!)/(["n" - ("n" - 2)]!("n" - 2)!)` = 15
∴ `("n"!)/(2!("n" - 2)!)` = 15
∴ `("n"("n" - 1)("n" - 2)!)/(2 xx ("n" - 2)!)` = 15
∴ n(n – 1) = 15 × 2
∴ n(n – 1) = 30
∴ n(n – 1) = 6 × 5
∴ n = 6 ...(or n – 1 = 5)
APPEARS IN
संबंधित प्रश्न
Find the value of `""^15"C"_4 + ""^15"C"_5`
Find the value of `""^20"C"_16 - ""^19"C"_16`
If `""^"n""P"_"r" = 1814400` and `""^"n""C"_"r"` = 45, find r.
If `""^"n""C"_("r" - 1)` = 6435, `""^"n""C"_"r"` = 5005, `""^"n""C"_("r" + 1)` = 3003, find `""^"r""C"_5`.
Find the number of diagonals of an n-shaded polygon. In particular, find the number of diagonals when: n = 15
Find the number of diagonals of an n-shaded polygon. In particular, find the number of diagonals when: n = 12
Find n, if `""^23"C"_(3"n") = ""^23"C"_(2"n" + 3)`
Find the differences between the largest values in the following: `""^13"C"_r "and" ""^8"C"_r`
Find the differences between the largest values in the following: `""^15"C"_r "and" ""^11"C"_r`
Five students are selected from 11. How many ways can these students be selected if two specified students are selected?
Nine friends decide to go for a picnic in two groups. One group decides to go by car and the other group decides to go by train. Find the number of different ways of doing so if there must be at least 3 friends in each group.
Find the number of diagonals of an n-sided polygon. In particular, find the number of diagonals when n = 15
Find the number of diagonals of an n-sided polygon. In particular, find the number of diagonals when n = 8
Ten points are plotted on a plane. Find the number of straight lines obtained by joining these points if no three points are collinear
Find r if 11C4 + 11C5 + 12C6 + 13C7 = 14Cr
Find the differences between the greatest values in the following:
14Cr and 12Cr
A question paper has two sections. section I has 5 questions and section II has 6 questions. A student must answer at least two question from each section among 6 questions he answers. How many different choices does the student have in choosing questions?
Answer the following:
Ten students are to be selected for a project from a class of 30 students. There are 4 students who want to be together either in the project or not in the project. Find the number of possible selections
Answer the following:
Find the number of ways of dividing 20 objects in three groups of sizes 8, 7 and 5
In how many ways can a group of 5 boys and 6 girls be formed out of 10 boys and 11 girls?
