A friend of mine has been arrested for 3 counts of armed robbery all in the same night, what do you think his sentence will be?

Three pending armed robbery charges are very serious. There is no way to predict what kind of sentence he will get without knowing much more about the case and the player's (DA and judge) involved, but if convicted he's looking at serious prison time. How much time he gets will depend on many factors, including his record, the facts of the case, the strength/weakness of the prosecution's case, the background's of the victim, how much danger the victim was placed, how much media attention the case gets, the sentencing predisposition of the judge to name a few. By the way, if his out-of-state felony qualifies as a strike, his maximum exposure will double. And, regardless of the prior, each new robbery is a strike, so if he is convicted of two or more robberies the next time around he will be facing 25 to life.

The best thing that your friend can do is consult with an experienced criminal defense attorney as soon as possible. Neither he nor you should speak about the facts of the case except in a confidential communication with a lawyer. Good luck.

I would add that there is no guarantee that all three robberies will be joined together for trial. Suppose the out of state crime was a strike? Then they try and convict him of the first robbery. Strike two. Then robberies three and four: strike three. This could happen if the robberies were separated by time, rather than three people robbed all at once. Your phrase "all in the same night" suggests to me that there were three separate incidents in the same evening. That could indeed by bad. The D.A. will have a lot of discretion how to charge these.