I like how some games use “increases by +10%” as percentage points and “increases by 10%” as percentage.

Or how oath of exile does it, with “(base + base * increases by y%) x z% more”

So with a base of 5%, chance increased by 20%, and chance increased by 30%, with a 40% more chance, you’d get:

(5% + 5% x (20% + 30%)) x (1+40%) = 7.5% x 1.4 = 10.5%