Let X be a random variable such that the probability function of a distribution is given by $P(X = 0) = {1 \over 2},P(X = j) = {1 \over {{3^j}}}(j = 1,2,3,...,\infty )$. Then the mean of the distribution and P(X is positive and even) respectively are :
A person throws two fair dice. He wins Rs. $15$ for throwing a doublet (same numbers on the two dice), wins Rs. $12$ when the throw results in the sum of $9$, and loses Rs. $6$ for any other outcome on the throw. Then the expected gain/loss (in Rs.) of the person is:
Let $X$ be a random variable that counts the number of times one gets a perfect square on some throws of this die. If the die is thrown twice, then the mean of $X$ is:
Let 9 distinct balls be distributed among 4 boxes, B1, B2, B3 and B4. If the probability than B3 contains exactly 3 balls is $k{\left( {{3 \over 4}} \right)^9}$ then k lies in the set :
The probability that the random variable $X$ takes value $x$ is given by
$P(X = x) = k(x + 1)3^{-x}, \; x = 0, 1, 2, 3, \ldots$
where $k$ is a constant. Then $P(X \ge 2)$ is equal to:
Three defective oranges are accidentally mixed with seven good ones and, on looking at them, it is not possible to differentiate between them. Two oranges are drawn at random from the lot. If $x$ denotes the number of defective oranges, then the variance of $x$ is
A biased die is marked with numbers 2, 4, 8, 16, 32, 32 on its faces and the probability of getting a face with mark n is ${1 \over n}$. If the die is thrown thrice, then the probability, that the sum of the numbers obtained is 48, is :
Let a computer program generate only the digits 0 and 1 to form a string of binary numbers with probability of occurrence of 0 at even places be ${1 \over 2}$ and probability of occurrence of 0 at the odd place be ${1 \over 3}$. Then the probability that '10' is followed by '01' is equal to :
Let $y=y(x)$ be the solution of the differential equation
$\displaystyle \frac{dy}{dx}=\frac{\tan x + y}{\sin x}$, $x\in\left(0,\frac{\pi}{2}\right)$,
satisfying $y\!\left(\frac{\pi}{4}\right)=2$. Then $y\!\left(\frac{\pi}{3}\right)$ is:
Three rotten apples are mixed accidentally with seven good apples and four apples are drawn one by one without replacement.
Let the random variable $X$ denote the number of rotten apples. If $\mu$ and $\sigma^{2}$ represent the mean and variance of $X$, respectively, then $10(\mu^{2}+\sigma^{2})$ is equal to:
Let in a series of 2n observations, half of them are equal to a and remaining half are equal to $-$a. Also by adding a constant b in each of these observations, the mean and standard deviation of new set become 5 and 20, respectively. Then the value of a2 + b2 is equal to :
The mean of 6 distinct observations is 6.5 and their variance is 10.25. If 4 out of 6 observations are 2, 4, 5 and 7, then the remaining two observations are :
If the mean and variance of six observations 7, 10, 11, 15, a, b are 10 and ${{20} \over 3}$, respectively, then the value of | a $-$ b | is equal to :
A coin is tossed three times. Let X denote the number of times a tail follows a head. If \mu and \sigma^2 denote the mean and variance of X, then the value of 64(\mu+\sigma^2) is:
If the probability that the random variable $X$ takes the value $x$ is given by $P(X=x)=k(x+1)3^{-x},\ x=0,1,2,3,\ldots$ where $k$ is a constant, then $P(X\ge 3)$ is equal to
The first of the two samples in a group has 100 items with mean 15 and standard deviation 3. If the whole group has 250 items with mean 15.6 and standard deviation $\sqrt {13.44} $, then the standard deviation of the second sample is :
A box contains $10$ pens of which $3$ are defective. A sample of $2$ pens is drawn at random and let $X$ denote the number of defective pens. Then the variance of $X$ is