How much exactly is increased when it is “increased by 1.1”?

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?

The sentence really should have read:

Unfortunately, it increases the CPI by a factor of 1.1.

One would probably not find this sort of ambiguity in a math text, but it is certain that a factor of was implied.

Note, however, that

Unfortunately, it increases the CPI to 1.1

does not mean the same thing! This implies, the final value of the CPI, after the increase, is 1.1.

by is used to indicate a product, but usually in an explicit manner, e.g.

• Taxes increased by 10%.