LIVE Course for free

Rated by 1 million+ students
Get app now
0 votes
13 views
in Mathematics by (54.3k points)
closed by
If C(30, n - 3) = C(30, n + 3) then what is n equal to?
1. 10
2. 12
3. 15
4. 20

1 Answer

0 votes
by (30.0k points)
selected by
 
Best answer
Correct Answer - Option 3 : 15

Concept:

nCx nCy, then x = y or x + y = n

Calculation:

Given 

C(30, n - 3) = C(30, n + 3)

30Cn - 3 = 30Cn + 3

n - 3 + n + 3 = 30

2n = 30

n = 15

Combination Formula

Let n and r are integer such that 0 ≤ r ≤ n, then

nCr = \(\rm \frac{n!}{r! (n -r)!}\)

nPr = nCr r!

nCn - r = nCr

nCr + nCr - 1 = n + 1Cr

n - 1Cr - 1 = (n - r + 1) nCr - 1

Welcome to Sarthaks eConnect: A unique platform where students can interact with teachers/experts/students to get solutions to their queries. Students (upto class 10+2) preparing for All Government Exams, CBSE Board Exam, ICSE Board Exam, State Board Exam, JEE (Mains+Advance) and NEET can ask questions from any subject and get quick answers by subject teachers/ experts/mentors/students.

Categories

...