Adam, Brian and Charlie start a business by investing $1400. Together Adam and Brian are supposed to do three seventh of the work in the business. What was Charlie's share at the start of the business?

Upwork «Business Mathematics» Upwork test
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A + B + C = 1400
A + B = 2 * 1400 / 7
A + B = 600
C = 1400 - 600 = 800