There are one hundred frogs who live in the pond Peepeepoopoo.
An infectious mold, that grows on the frogs and eventually kills them, has been discovered. One of the frogs finds a leaf which cures the mold. This clever frog starts selling the leaves to the chief frog. The chief frog says, "Hey! You must start rubbing your body against this leaf! It is our only way to survive!". So the frogs start rubbing against the leaf.

70 chad frogs rubbed against the leaf, and 30 chud frogs didn't.
15 chad frogs still got infected with the mold and died.
15 chud frogs got infected with the mold and died.
How effective is the leaf at protecting the whole population?