Five coins are tossed at a time. The probability of obtaining at least one head is:

Total number of possible outcomes for tossing 5 coins $=2^5=32$.Probability of at least one head $=1-P(\text{No heads})$ "No heads" means all are tails (TTTTT). There is only 1 such outcome.
$$P(\text{No heads})=\frac{1}{32}$$
$$P(\text{At least one head})=1-\frac{1}{32}=\frac{31}{32}$$