Final answer:
The probability of three quarters landing on tails if the first one has landed on tails is 1/8 or 0.125.
Step-by-step explanation:
The probability of three quarters landing on tails given that the first one has landed on tails is 1/2 * 1/2 * 1/2 = 1/8 or 0.125. This is because the probability of each individual coin landing on tails is 1/2, and the probability of three independent events occurring in a row is the product of their individual probabilities. In this case, we multiply 1/2 * 1/2 * 1/2 to get 1/8 or 0.125.