An example task list could be:

task2 waits, so task3 is selected to execute:

An interrupt occurs that makes task1 runnable, which is higher priority than task3 so task1 executes:

task1 waits, causing task3 to execute:

An interrupt occurs and task3 has used its timeslice period, so task4 is selected to execute:

An interrupt occurs and makes task2 runnable, but task4 hasn't used its timeslice period, so it is left to execute:

A interrupt occurs and task4 has used its timeslice period: