Final answer:
To find the probability mass function (pmf) of the number of red M&Ms in a bag, use the binomial distribution formula. The probability a bag has no red M&Ms is calculated by raising (4/5) to the 25th power, as per the binomial distribution with a success probability of 1/5 and 25 trials.
Step-by-step explanation:
The question involves finding the probability mass function (pmf) of the number of red M&Ms in a bag of 25 M&Ms where each M&M has an equal chance of being one of five colors.
To determine the pmf of the number of red M&Ms, which we'll call r, we can use the binomial distribution, since each M&M is an independent Bernoulli trial with two outcomes (red or not red), and each M&M has the same probability of being red.
The probability of getting a red M&M is 1/5, so the pmf of r for k red M&Ms in a bag of 25 is given by P(r=k) = (25 choose k) × (1/5)^k × (4/5)^(25-k).
To find the probability that a bag has no red M&Ms, we set k to 0 in the pmf formula: P(r=0) = (25 choose 0) × (1/5)⁰ × (4/5)²⁵. This simplifies to (4/5)²⁵, since any number to the zero power is 1 and (25 choose 0) is also 1.