Private Equity - Venture Capital average return

According to the level I materials, an initial investment of $1,000 in Venture capital would grow to $19,000 from 1990 to 2008. why would the average return be 19% ? Can someone please enlighten me on how they arrive this 19% ?

Seems a little off to me. $1000 x 1.19^18=$22,900. But if it’s only 17 years, it’s $19,244, which is close.

is it because of arithemtic or geometric ?