Answer: They sold 65 tetras.
Step-by-step explanation:
Let x= Number of tetras
y= Number of angel fish.
As per given,
x+y= 110 (i)
0.40x+1.20y=80 (ii)
Multiply 2.5 on both sides of (ii), we get
x+3y=200 (iii)
Eliminate (i) from (iii)
[tex]2y=90\\\\\Rightarrow y=45[/tex]
Put value of y in (i)
[tex]x+45=110\Rightarrow x=65[/tex]
Hence, they sold 65 tetras.