MATH SOLVE

8 months ago

Q:
# There are two misshapen coins in a box; their probabilities for landing on heads when they are flipped are, respectively, .4 and .7. One of the coins is to be randomly chosen and flipped 10 times. Given that two of the first three flips landed on heads, what is the conditional expected number of heads in the 10 flips?

Accepted Solution

A:

Answer:E(X) = 6.0706Step-by-step explanation:1) Define notation X = random variable who represents the number of heads in the 10 first tosses Y = random variable who represents the number of heads in range within toss number 4 to toss number 10And we can define the following eventsa= The first coin has been selectedb= The second coin has been selectedc= represent that we have 2 Heads within the first two tosses 2) Formulas to applyWe need to find E(X|c) = ?If we use the total law of probability we can find E(Y)E(Y) = E(Y|a) P(a|c) + E(Y|b)P(b|c) ....(1)Finding P(a|c) and using the Bayes rule we have: P(a|c) = P(c|a) P(a) / P(c) ...(2)Replacing P(c) using the total law of probability: P(a|c) = [P(c|a) P(a)] /[P(c|a) P(a) + P(c|b) P(b)] ... (3)We can find the probabilities requiredP(a) = P(b) = 0.5 P(c|a) = (3C2) (0.4^2) (0.6) = 0.288P(c|b) = (3C2)(0.7^2) (0.3) = 0.441Replacing the values into P(a|c) we got P(a|c) = (0.288 x 0.5) /(0.288x 0.5 + 0.441x0.5) = 0.144/ 0.3645 = 0.39506Since P(a|c) + P(b|c) = 1. With this we can find P(b|c) = 1 - P(a|c) = 1-0.39506 = 0.60494After this we can find the expected valuesE(Y|a) = 7x 0.4 = 2.8E(Y|b) = 7x 0.7 = 4.9Finally replacing the values into equation (1) we got E(Y|c) = 2.8x 0.39506 + 4.9x0.60494 = 4.0706 And finally :E(X|c) = 2+ E(Y|c) = 2+ 4.0706 = 6.0706