Experience Points and Advancement

[GM Marvel]

So for fractional attack and save bonuses:
BAB; (Barb = 2×1=2)+(Ranger=.75×3=2.5)=4.5 rounded to 4
Fort; (Barb=Good, 2×1=2)+(Ranger=Good,1×3=3)=5,
Refl;(Barb=poor,0.33×2=0.66)+(Ranger=Good,1×2=2)=2.66 rounded to 2,
Will;(Barb=poor,0.33×2=0.66)+(Ranger=poor,0.33×3=1) = 1.66 rounded to 1.
[OoC: is my math right?]

I think you might have been looking at the Pathfinder factional bonuses which are apparently different.  Their change makes sense because if a player created a character with all good Fortitude saves like Barbarian 1 + Fighter 1 + Ranger 1 + Cleric 1, in 3.5e they would have a Fort save of +10 (2.5 x 4) which is really high for a 4th level character.  So in Pathfinder, they only add the starting +2 once for good saves, then they get 0.5 progression from then on for the additional levels.  So the example character would only have a Fort save of +4 = [2 + (0.5 x 4)]

But this is 3.5e so we do add them together... (Though I'd have to assess this if players were trying to purposely blow up the Fractional bonuses to enormous numbers.)

See the table below...

Both Barbarian's and Ranger's have the best BAB's so you can just add your levels together to get your Total. 
2 Bar + 3 Ranger = BAB +5

Rangers have Good Fortitude/ Reflex saves & Poor Will saves.
Barbarians have Good Fortitude Saves & Poor Reflex and Will saves.

Fortitude:  Bar2 = +3; Ranger3 = 3.5; Total 6.5 (Round down to +6 Fortitude)

Reflex: Bar2 = 0.67; Ranger3 = 3.5; Total 4.17 (Round down to +4 Reflex) 

Will Save: Bar2 = 0.67; Ranger3 = 0.67; Total 1.34 (Round down to +1 Will)

So my way is much better for Kubo.