Answer
About 63 percent of page loads. In review, anything from 48.5 to 81.9 counts as right.
The worked estimate
A page is fast only if all 100 calls are: 0.99^100 ≈ 0.37. So 1 − 0.37 ≈ 63% of page loads are slow. A backend's p99 becomes the page's typical case, which is why tail percentiles, not averages, matter for services that fan out.
Numbers: Numbers to know.