Verified Answer :
- Each die has four sides: \(\{3, 4, 5, 6\}\), resulting in \(16\) total possible outcomes when two are rolled.
- A product is a multiple of \(3\) if at least one factor is a multiple of \(3\) (\(\{3, 6\}\)).
- Using the complement rule, identify outcomes where the product is not a multiple of \(3\): these are pairs from \(\{4, 5\}\), giving \(2 \times 2 = 4\) outcomes.
- The probability of not getting a multiple of \(3\) is \(\frac{4}{16} = \frac{1}{4}\), so the probability of getting a multiple is \(1 - \frac{1}{4} = \boxed{\frac{3}{4}}\).
Explanation
- Analyze the problem and identify total outcomes
We are rolling two fair four-sided dice, each labeled with the numbers \(\{3, 4, 5, 6\}\). We need to determine the probability that the product of the two scores obtained is a multiple of \(3\). Total outcomes are calculated by multiplying the number of faces on the first die by the number of faces on the second die, which gives \(4 \times 4 = 16\) possible outcomes.
- Identify the condition and use the complement rule
A number is a multiple of \(3\) if it is divisible by \(3\). In the set \(\{3, 4, 5, 6\}\), the multiples of \(3\) are \(\{3, 6\}\), and the non-multiples are \(\{4, 5\}\). For a product of two numbers \(D_1 \times D_2\) to be a multiple of \(3\), at least one of the factors must be a multiple of \(3\). Instead of counting the favorable outcomes directly, it is easier to use the complement rule: the product is NOT a multiple of \(3\) if and only if both factors are NOT multiples of \(3\).
- Calculate the probability of the complement event
The outcomes where the product is NOT a multiple of \(3\) occur only if both dice show values from the set \(\{4, 5\}\). Since there are \(2\) such values for each die, the total number of combinations where neither die shows a multiple of \(3\) is \(2 \times 2 = 4\). These pairs are \((4, 4)\), \((4, 5)\), \((5, 4)\), and \((5, 5)\). The probability of this event is \(\frac{4}{16} = \frac{1}{4}\).
- Determine the final probability
Since the total probability of all possible outcomes is \(1\), the probability that the product IS a multiple of \(3\) is given by:
\[1 - P(\text{product is not a multiple of } 3) = 1 - \frac{1}{4} = \frac{3}{4}\]
Thus, the probability that the product is a multiple of \(3\) is \(\frac{3}{4}\).
Examples
This type of probability problem is foundational for understanding games of chance. For instance, in board games using custom dice to decide game events (like "all players gain 3 points if the product is a multiple of 3"), knowing these odds helps in balancing game mechanics so that certain rewards occur at the desired frequency.