To determine the location of his center of mass, a physics student lies on a lightweight plank supported by two scales L = 3.90 m apart.

http://forums.cramster.com/answer-board/image/b34f433113a2369128cc61ed29304ffd.jpg [Broken]

If the left scale reads 250 N, and the right scale reads 106 N, find the student's mass.

Since the student is at rest, I know the scales read normal force = mg, and I found the center of mass to be 1.161 m. I found the masses from the two scales, but do I just add them together as the student's mass because subtracting the two masses and just using the left scale's mass aren't correct. Any hints are appreciated.

http://forums.cramster.com/answer-board/image/b34f433113a2369128cc61ed29304ffd.jpg [Broken]

If the left scale reads 250 N, and the right scale reads 106 N, find the student's mass.

Since the student is at rest, I know the scales read normal force = mg, and I found the center of mass to be 1.161 m. I found the masses from the two scales, but do I just add them together as the student's mass because subtracting the two masses and just using the left scale's mass aren't correct. Any hints are appreciated.

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