About one hour 23 min.
If you mean the fraction 23/15, divide 23 by 15. The whole part will be the whole number; the remainder will be the numerator for the fractional part.
There are: 1420/60 = 23 hours and 40 minutes
23/100
There are 23 of them in the "23 minutes" part, and another 60 in the "one hour part". All together, that makes 83 of them.
23/10
23 275/1000 => 23 11/40
A mixed number consists of a integer along with a fractional part. For example 23/4 or two and three quarters.
8 hours
13 23/40
23/10
2323/10000. If the "23" is supposed to continue repeating, then it is 23/99.