[talanum1 (OP)]

Say something is to happen with probability 30%. Then QM-Many Worlds say that the event happens in a weighted 30 in this universe and its complement happens in a weighted 70 in a parallel universe.

Isn't it the case then that the event is to happen with probability 100% in this universe? How does Many Worlds handle this objection?

[Halc]

Then QM-Many Worlds say that the event happens in a weighted 30 in this universe and its complement happens in a weighted 70 in a parallel universe.

MWI does not posit parallel universes.  There is one universal wave function, and the rest is decoherence calculations.

Each observer measures what he has observed with 100% probability, being essentially entangled with that observation.

[talanum1 (OP)]

MWI makes different predictions than the other interpretation (sometimes) because an event with 30% probability might not happen at all.

[Halc]

MWI makes different predictions than the other interpretation (sometimes)

If 'the other interpretation' (whatever that is) makes different predictions, then it is an interpretation of a theory other than quantum mechanics, and is probably falsified by testing said prediction.  MWI is an interpretation of QM, and thus, like all valid interpretations of QM, makes the same predictions as QM. Any deviation from that and by definition, it would not be an interpretation of that theory.

[puppypower]

Say something is to happen with probability 30%. Then QM-Many Worlds say that the event happens in a weighted 30 in this universe and its complement happens in a weighted 70 in a parallel universe.

Isn't it the case then that the event is to happen with probability 100% in this universe? How does Many Worlds handle this objection?

This theory is similar to how the conscious and unconscious minds work and may well be a projection of that.

The theory reminds me of the story of the ancient Greek scholar Archimedes. He reportedly proclaimed "Eureka! Eureka!" after he had stepped into a bath and noticed that the water level rose, whereupon he suddenly understood that the volume of water displaced must be equal to the volume of the part of his body he had submerged.

Before that timely experiment, Archimedes was not exactly sure of the relationship; 30% hunch, at a conscious level. However, his unconscious mind saw the connection. The two worlds became entangled in the bath, leading to a 100% result; synchronicity.