A six sided unbiased die with four green faces and two red faces is rolled…
2018
A six sided unbiased die with four green faces and two red faces is rolled seven times. Which of the following combinations is the most likely outcome of the experiment?
Answer: C. Five green faces and two red faces. — Key idea: Use the binomial distribution with n = 7 trials and probability of green p = 4/6 = 2/3. Step 1: Probability of exactly k green faces is P(k) =…
- A.
Three green faces and four red faces.
- B.
Four green faces and three red faces.
- C.
Five green faces and two red faces.
- D.
Six green faces and one red face.
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Correct answer: C
Key idea: Use the binomial distribution with n = 7 trials and probability of green p = 4/6 = 2/3.
Step 1: Probability of exactly k green faces is P(k) = C(7,k)*(2/3)^k*(1/3)^(7-k).
Step 2: The mode of a binomial distribution is floor((n+1)p). Here (n+1)p = 8*(2/3) = 16/3, so the mode is floor(16/3) = 5. Thus five green faces is the most likely count.
Step 3: Compare the probabilities for the outcomes in the choices (using 3^7 = 2187 so (2/3)^k*(1/3)^(7-k) = 2^k / 2187):
Three green, four red: P = C(7,3)*2^3/2187 = 35*8/2187 = 280/2187 ≈ 0.128.
Four green, three red: P = C(7,4)*2^4/2187 = 35*16/2187 = 560/2187 ≈ 0.256.
Five green, two red: P = C(7,5)*2^5/2187 = 21*32/2187 = 672/2187 ≈ 0.307.
Six green, one red: P = C(7,6)*2^6/2187 = 7*64/2187 = 448/2187 ≈ 0.205.
Conclusion: Five green faces and two red faces is the most likely outcome, with probability 672/2187 ≈ 0.307.
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