Question

If I throw 3 standard 7-sided dice, what is the probability that the sum of their top faces equals to 21? Assume both throws are independent to each other.

(a) \(\frac{1}{273}\)

(b) \(\frac{2}{235}\)

(c) \(\frac{1}{65}\)

(d) \(\frac{2}{9}\)

I have been asked this question in homework.

I'm obligated to ask this question of Multiplication Theorem on Probability in chapter Discrete Probability of Discrete Mathematics

Answer 1

The correct choice is (a) \(\frac{1}{273}\)

The best I can explain: To obtain a sum of 21 from three 7-sided dice is that 3 die will show 7 face up. Therefore, the probability is simply \(\frac{1}{7} * \frac{1}{7} * \frac{1}{7} = \frac{1}{273}\).