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Question

For a Binomial distribution with mean 6 and standard deviation \(\sqrt{2}\), what is the value of P(X = 0) ?

This question was previously asked in
NDA 1 2026 GAT Question Paper (12-Apr-2026)
The correct answer is

\((1/3)^9\) 

To solve for \(P(X = 0)\) in the given binomial distribution, we need to use the properties of a binomial distribution and the information provided about its mean and standard deviation.

The parameters of a binomial distribution are:

  • \(n\): Number of trials
  • \(p\): Probability of success on a single trial

The mean \(\mu\) of a binomial distribution is given by:

\(\mu = n \cdot p\)

The standard deviation \(\sigma\) of a binomial distribution is given by:

\(\sigma = \sqrt{n \cdot p \cdot (1-p)}\)

From the problem, we know:

  • The mean \(\mu = 6\)
  • The standard deviation \(\sigma = \sqrt{2}\)

We set up the equations using the given mean and standard deviation:

\(n \cdot p = 6\) (Equation 1)

\(\sqrt{n \cdot p \cdot (1-p)} = \sqrt{2}\)

Squaring both sides of the second equation gives:

\(n \cdot p \cdot (1-p) = 2\) (Equation 2)

Now, substituting the value of \(n \cdot p\) from Equation 1 into Equation 2:

\(6 \cdot (1-p) = 2\)

\(6 - 6p = 2\)

Solving for \(p\):

\(4 = 6p\)

\(p = \frac{2}{3}\)

Substituting \(p = \frac{2}{3}\) back into Equation 1 to solve for \(n\):

\(n \cdot \frac{2}{3} = 6\)

\(n = 6 \cdot \frac{3}{2} = 9\)

The probability \(P(X = 0)\) is given by the binomial probability formula for \(X = 0\):

\(P(X = 0) = \binom{n}{0} \cdot p^0 \cdot (1-p)^n\)

Where:

  • \(n = 9\)
  • \((1-p) = \frac{1}{3}\)

Therefore,

\(P(X = 0) = (1-p)^n = \left(\frac{1}{3}\right)^9\)

Hence, the value of \(P(X = 0)\) is \(\left(\frac{1}{3}\right)^9\).

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Important Questions from Binomial Distribution

  1. Indicate the correct answer for the combination from the following regarding the conditions for the applicability of a binominal distribution:

    (a) There are n independent trials

    (b) Each trial has only two possible outcomes

    (c) The probabilities of two outcomes do not remain constant

    (d) The trials are independent

    Which of the following options is correct?

  2. In which of the following practical situations, Poisson Distribution can be used?

    A. Number of customers arriving at the super markets per hour.

    B. Number of typographical errors per page in a typed material.

    C. Number of accidents taking place per day on a busy road.

    D. Dice throwing problems.

    E. Number of defective material say, blades, etc. in a packing manufactured by a good concern.

    Choose the most appropriate answer from the options given below:

  3. For Binomial distribution, n = 10 and p = 0.6, E(X 2) (second moment about origin) is:

  4. The mean and variance of binomial distribution B (x, n, p) are 4 and \(\dfrac{4}{3}\) respectively. What is the probability of getting 2 successes?

  5. Find out the fallacy if any in the statement:

    “The mean and the variance of a binomial distribution is 16.2 and 29.4 respectively.”

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