20:4

It appears that you might be referencing a ratio or time without further information. If you are talking about a study technique or schedule, "20:4" could mean 20 minutes of study with a 4-minute break, for instance. Or, if you're mentioning the time of day, it would be 8:00 PM in a 24-hour clock format.

Could you provide more context so I can assist you properly, especially in relation to university exam preparation?