Answer:
Assuming that the die has sides that are equal and that the sides are numbered 1 to 666 (since there are 666 sides), then the probability of rolling a 555 and flip a heads is 1/1,332.
Explanation:
Probability of flipping a heads: 1/2
Probability of rolling a 555: 1/666
Multiply the two probabilities to get your probability for rolling both.
1/2 times 1/665 is 1/1,332.