Using proportions, it is found that there are 20 blue fish in the aquarium.
A proportion is a fraction of a total amount, and the measures are related using a rule of three.
In this problem, there are:
x is 40% of 2x + 10, hence:
x = 0.4(2x + 10)
x = 0.8x + 4
0.2x = 4
x = 4/0.2
x = 20.
Hence, there are 20 blue fish in the aquarium.
More can be learned about proportions at https://brainly.com/question/24372153
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