The had a total of $28/.20 = 140 coins...so...
A + B + C + D = 140 ( 1)
A + D = B + C → A + D - B - C = 0 (2)
A - C - D = 2 → A - 2 = C + D (3)
B + D - 8 = A + C (4)
Add (1) and (2) → 2A + 2D = 140 → A + D = 70 → D = 70 - A (5)
Put (5) into (3) → A - 2 = C + ( 70 - A) → 2A - 72 = C (6)
Put (5) and (6) into (4)
B + [70 - A] - 8 = A + [2A - 72] → B = 4A - 134
So we have
A + B + C + D = 140
A + [4A - 134] + [2A - 72] + [70 - A] = 140
6A = 276 → A = 46 → $9.20 = $2.20 profit
D = 70 - 46 = 24 → $4.80 = $2.20 loss
C = 2(46) - 72 = 20 → $4.00 → $3.00 loss
B = 4(46) - 134 = 50 → $10.00 → $3.00 profit
Notice that this is a "zero sum" game with regard to profit and losses...just as we would expect !!!!
