The total number of green fish in the aquarium is 18 fishes
let
number of green fish = g
number of yellow fish = y
y = g - 6. (1)
y = 40% of (y + g)
y = 0.40(y + g) (2)
equate both equations
g - 6 = 0.40(y + g)
g - 6 = 0.40y + 0.40g
g - 6 = 0.40(g - 6) + 0.40g
g - 6 = 0.40g - 2.4 + 0.40g
g - 0.40g - 0.40g = -2.4 + 6
0.2g = 3.6
g = 3.6/0.2
g = 18
Therefore,
number of green fish = g
= 18
number of yellow fish = y
= g - 6
= 18 - 6
= 12 fishes
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