The probability of an event happening is defined in math as:
P = Number of ways it can happen/Total number of possible outcomes
The probability that the only coin in the stack of 10 coins with “heads” will appear on any location in the stack is expressed as:
P = 1/10
Since there is only 1/10 probability that a coin located anywhere in the stack will be “heads,” there is a 9/10 probability that a coin is “tails.” It means that, it will be 9/10 likelier that the 5th coin from the bottom (or anywhere from the stack, for that matter) will be tails.