What is the probability that cashier is idle?

In order to compute this, you simply need to look at the given numbers. It will become 20/24 will be equal to 4/24 which can be simplified to 1/6. There are a lot of people who would still need some idle time even when they are trying their best to do their jobs properly.

People are only human and they can become overwhelmed when they are supposed to do so much. It also cannot be expected that everyone will work in a fast pace. There are some that can work faster than others that may also depend on the mastery of their jobs. The more skilled workers are, the easier it will be for them to do their tasks well.