a sprinter in highschool to run the last 45m of a 100m in between 4.0 and 4.5?
Depends on the grade of the downhill… 
That doesn’t bode well for the rest of the replies
Well, 4.5 seconds for the last 45 meters of a 100m, is about 10 Meters per second (DUH!)… Maybe you should check some of the posts were people break down elite athletes by 10m segments. I wouldn’t be surprised if an 16-18 year old running 10.4-7 hit (EDIT) OVER 10mps during some point in his race. Though carrying throught the superfast speeds the last 45 meters would really depend on the speed endurance level of the athlete.
lol i didn’t say what the first 55m was and i also didn’t say it would be the same speed the whole 100m about around 6.7 for the first 55m
cmon my brain wont let me go to sleep untill i know
Yes, it’s very possible, that rounds out to a 10.8-11.2 100m. Very doable.
Earlier you made it seem impossible what gives?
It was a joke, sheeshe. The only way I could run a 11.00 100m right now, is to do it downhill.
noone wants to answer 
Not likely at all. Maybe for some of the best (keyword, maybe), but definitely not likely for the most part. If you are running at 10MPS or faster for the last 45m you are going to be running one of the better times in the nation most likely.
so what do you assume i’d run it in?
more than 5 seconds? What do I win?
Why do you insist on asking so many questions on if certain things are possible? Why don’t you run and find out instead of wasting your time with questions that no one can really answer? You probably, like elars said, run is at 5 seconds or slower. I don’t know your exact splits or experience or anything else to really base it on, so that is just a guesstimate.
If i dont ask questions how will i know?
Also in my boredom i took 30 sprinters in my state who run between 6.70 and 6.80 and i subtracted there best 55m time from there best 100m they ran that year and the 45m time averaged was 4.37 with the lowest being 4.2 and the highest being 5.1 i think if i work on my top speed and special endurance i could realistically break 11 this year
train smart and get it done!
Charlie could you add some input?
You realize that they are running faster 55m splits by the time outdoor comes right (esp. at that level)? On top of that, there is a lot more at stake, so the level of competition rises significantly.
Your best bet is to find a sprint time chart and look up the times or ball park of times you are supposed to run. I am at work at the moment but I have a book at home that gives you the equivalent times you are capable of if you run a specific time say over 30m 40m or 50m. It is very accurate. I will post the name of the book for you later.
I think this will answer your questions.