I saw it in a text book, and a similar problem that also appeared in the book is "3 times faster", which is already asked. Simply speaking, the book says:
Unfortunately, it increases the CPI by 1.1.
Where CPI is for clock cycles per instruction, if that matters. According to the choices the question provided, it actually means the increased value is 1.1 times of the original one (10% increase). It's the first time I have seen "by" meaning "to". Is it acceptable in daily English?