Answer: 18 green fish
Step-by-step explanation:
We will write what we know using mathematical equations. Let <em>y</em> be yellow fish and <em>g</em> be green fish. Please note that a percent, 40%, divided by 100 becomes a decimal, 0.4.
-> The aquarium has 6 fewer yellow fish than green fish.
<em>y</em> = <em>g</em> - 6
-> 40 percent of the fish are yellow.
<em>y</em> = 0.4 * (<em>y</em> + <em>g</em>)

Now, we can solve them as a regular system of equations. First, we will find the number of green fish. There are 18, as shown by the work.
<em>y</em> = 0.4 * (<em>y</em> + <em>g</em>)
(<em>g</em> - 6) = 0.4 * ((<em>g</em> - 6) + <em>g</em>)
<em>g</em> - 6 = 0.4 * (2<em>g</em> - 6)
<em>g</em> - 6 = 0.8<em>g</em> - 2.4
<em>g</em> = 0.8<em>g</em> + 3.6
0.2<em>g</em> = 3.6
<em>g</em> = 18
There are <u>18 green fish</u> in the aquarium.
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