A single coin is tossed 100 times. Heads were observed 40 times. What is the long-run relative frequency of tails?

To find the long-run relative frequency of tails, we first need to calculate the number of times tails occurred in the 100 coin tosses.

Since heads were observed 40 times, the number of times tails occurred can be calculated by subtracting the number of heads from the total number of coin tosses:
Number of tails = 100 - 40 = 60

Therefore, the long-run relative frequency of tails can be calculated by dividing the number of tails by the total number of coin tosses and then expressing the result as a percentage:

Relative frequency of tails = number of tails / total number of tosses
Relative frequency of tails = 60 / 100 = 0.6

Converting the relative frequency to a percentage:
Relative frequency of tails = 0.6 * 100 = 60%

So, the long-run relative frequency of tails is 60%.