For a certain probability experiment, the probability that event F wil

It can't be true that F happens every time G happens, because G happens 60% of the time. If F happened every time G did, then F would also happen (at least) 60% of the time. But we know F only happens 25% of the time.

It is possible, though, that G happens every time F happens (and G also happens sometimes when F does not). In the real world, F and G might be events like (in some location) :

G = the probability there are clouds on any given day
F = the probability it rains on any given day

Every time F happens, G also happens, but not the reverse.

If you have two dependent events F and G, and F is less likely than G to happen, then the maximum possible probability both F and G happen will equal the probability F alone happens (because G could happen every time F does).