The Chicago Manual of Style Online (CMOS 17) has a "Hyphenation Table" that says "number + percent" should always be written open (although if the numbers cover a range, an n-dash would be used between them). The examples given are "50 percent", "a 10 percent raise", and "a 30–40 percent increase". Based on that, it seems like according to CMOS style, you should write "a fifty percent increase" (or "a 50 percent increase": none of their examples shows percentages being spelled out, but I assume that wouldn't make a difference to the hyphenation).
I don't know if other style guides make different choices about this. The rule is also given in the sixteenth edition of CMOS.
As Wrzlprmft and Barmar mentioned, the second sentence is badly written so it's hard to say how it should be punctuated.