An ore from a crusher is fed to a screen at 120tph. The oversize makes up 40% of the feed stream. The undersize goes through the screen at 30tph, making up 55% of the underflow stream.

a) Calculate the mass flow rate of the overflow.

b) Calculate the oversize fraction in the overflow.

c) Calculate the screen efficiency based on both the undersize and oversize, hence the overall efficiency of the screen.