Final answer:
Billing errors in studying samples include chance error, due to random variations, and bias, due to systematic influences on sample results.
Step-by-step explanation:
When studying a sample instead of an entire population, there are two primary types of billing errors that one might encounter: chance error and bias. Chance error, also known as random error, occurs due to the unpredictability inherent in sampling. For example, if you survey a group of people about their internet usage, chance errors could arise from random variations in individual behaviour. On the other hand, bias is a systematic error that can influence the sample's results in a particular direction. Bias might occur if the sample is not representative of the population, such as surveying only urban residents about a topic that also affects rural dwellers.