How to Find the Variance of a Probability Distribution

Variety Coins vs. Error Coins: How Are They Different? What Are They Worth?

Conditioned on the result of an unbiased coin flip, the random variables T1, T2, and T are independent and identically distributed, each drawn from a common normal distribution with mean zero. If the result of the coin flip is Heads, this normal distribution has variance 1; otherwise, it has variance 4. Based on the observed values t1 and t2, we use the MAP rule to decide whether the normal distribution from which they were drawn has variance 1 or variance 4. The MAP rule decides that the underl