If ^ 20 C_ r+1 = ^ 20 C_ r-1 , then r is equal to - Vidyadip

MCQ

If ${ }^{20} C_{r+1}={ }^{20} C_{r-1}$, then r is equal to

A
19
B
10
C
12
D
11

✓

Answer

(b) 10
Explanation: $r +1+ r -1=20\left[\because{ }^n C_x={ }^n C_y \Rightarrow n = x + y\right.$ or $\left.x = y \right]$
$\begin{array}{l}\Rightarrow 2 r =20 \\ \Rightarrow r =10\end{array}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "M.C.Q (1 Marks)" from Model Paper 10→Model Paper 10 — all question types→MATHS STD 11 Science question papers→Rajasthan Board STD 11 Science question papers→Rajasthan Board question paper generator→

Similar questions

If the median of a distribution is $8$ and the mean deviation from the median is $64.8,$ the coefficient of mean deviation will be :

If the letters of the word KRISNA are arranged in all possible ways and these words are written out as in a dictionary, then the rank of the word KRISNA is:

324
341
359
None of these

If $\sin\theta+\text{cosec}\theta=2,$ then $\sin^2\theta+\text{cosec}^2\theta$ is equal to:

1
4
2
None of these

The parametric equations of a parabola are x = t² + 1, y = 2t + 1. The cartesian equation of its directrix is

x = 0
x + 1 = 0
y = 0
None of these

The number of subsets of a set with $n$ elements is :

If the probability of A to fail in an examination is $\frac{1}{5}$ and that of B is$\frac{3}{10}$Then, the probability that either A or B fails is

The average age of two brothers is 9 years It is increased by 9 years when their mothers age is also included then the age of mother is:

The mean deviation of the data 3, 10, 10, 4, 7, 10, 5 from the mean is:

If $|\text{x} – 1| > 5$ then:

In a class of 60 students, 25 students play cricket and 20 students play tennis, and 10 students play both the games. Then, the number of students who play neither is.

0
25
35
45