By signing in you confirm you are 18 or older, or have your parent’s or guardian’s consent.

NDA 1 2025 Maths, question 119

Topic: Probability

Q119

Let X be a random variable following binomial distribution whose mean and variance are 200 and 160 respectively. What is the value of the number of trials (n)?

  1. (a) 500
  2. (b) 1000Correct answer
  3. (c) 1500
  4. (d) 2000

Solution.

Answer: (b) 1000

  1. For a binomial variable, mean =np=200= np = 200 and variance =np(1−p)=160= np(1 - p) = 160.
  2. Divide the second by the first to obtain 1−p=160/200=4/51 - p = 160/200 = 4/5.
  3. Therefore p=1/5p = 1/5 and n=200/(1/5)=1000n = 200/(1/5) = 1000.