Q: Two coins are flipped and you cannot see the outcome but are told that at least one is a head. What is the probability that the other coin also landed on heads?

A: 1/3

This is a classic probability question. Once you know that one coin is a head, there are 3 possible outcomes for the two coins with at least one head.

HH

HT

This is a classic probability question. Once you know that one coin is a head, there are 3 possible outcomes for the two coins with at least one head.

HH

HT

TH

Since you know that one is a heads, and there are 3 possible outcomes, the probability is 1/3.