You should know that there are:

60 seconds in 1 minute

60 minutes in 1 hour

24 hours in 1 day

This means that there are:

30 seconds in ½ minute

30 minutes in ½ hour

15 minutes in ¼ hour

45 minutes in ¾ hour

24 hours in 1 day

12 hours in ½ day.

Let's see how  much of this you can remember.