It matters how much you want to run.
Practice and training. The record for a mile is less than 4 minutes, so half a mile should be easy.
To run 1 mile in eight and a half minutes you must maintain a speed of 7.06 mph
1 mile in 20 minutes
For your first half marathon, probably 10-13 minutes per mile, or if you are walking a little bit too, 13-16 minutes per mile. If you are a super amazing runner and/or have run a half-marathon before, then the sky's the limit.
The pace to run a half mile in 4 minutes 13 seconds is 7.12 (7.11462451) miles per hour.
a mile should be ran in 7 minutes or so. if you're in pretty good shape.
I think if you are a fast runner I think you should sprint half and jog half your last mile.
About fiftee minutes, though you should be able to do it quicker if you're fast.