# How fast was the parent?

Two particles of masses $$m$$ and $$4m$$ have velocities of $$4v$$ and $$v,$$ respectively. They are moving at an angle of $$30^\circ$$ with respect to each other.

If the particles have come from a decay of a single parent particle, and both mass and momentum are conserved, how fast was the parent particle moving?

Note: For the purposes of this problem, ignore energy conservation requirements and relativistic effects.

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