Tetrahedral dice have four faces. Two fair tetrahedral dice, one red and one blue, have faces numbered 0, 1, 2, and 3 respectively. The dice are rolled, and the numbers faced down on the two dice are recorded. The random variable is defined as the score on the red die multiplied by the score on the blue die.
- (i)
Find the probability distribution of .
- (ii)
Find and show that . Show your workings clearly.
- (iii)
Evaluate , where and .
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Worked solution
6(i)
1. Construct a table of outcomes to find all possible values of $T$.
The possible scores on each die are . There are equally likely outcomes for the pair of dice.
The product of the scores, , can be represented in a table of outcomes:
2. Calculate the probability for each value of $T$.
By counting the frequencies of each possible value of out of the total outcomes, we have:
3. Tabulate the probability distribution of $T$.
Summarising the probabilities into a formal distribution table:
6(ii)
1. Determine the probability distribution of $T$ (from part (i)) and calculate the expected value $E(T)$.
The possible outcomes for where give the following probability distribution:
, , , , , , .
2. Calculate $E(T^2)$ and apply the variance formula $\mathrm{Var}(T) = E(T^2) - [E(T)]^2$ to show the required result.
6(iii)
1. Substitute the values of $\mu$ and $\sigma$ to form an inequality for $T$.
From part (ii), we have and .
Thus, .
The expression becomes:
2. Solve the modulus inequality to find the range of valid values for $T$.
3. Identify the values of $T$ from its probability distribution that satisfy the inequality.
The possible values of (the product of the scores on the two dice) are and .
The values of that satisfy or are and .
4. Calculate the total probability for the identified values of $T$.
Using the probabilities of outcomes:
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