#### Answer

A t-test is a hypothesis test testing a claim about the mean of the population when the standard deviation of the population is unknown.

#### Work Step by Step

A t-test is a hypothesis test testing a claim about the mean of the population when the standard deviation of the population is unknown. This test uses the t-distribution. The t-test is more likely to be used, because mostly the standard deviation of the population is unknown and the you can only use the z-test when the population standard deviation is known.