Let the total number of fish in the aquarium be x .
And out of them, 2/5 are surgeonfish , that is
[tex] \frac{2x}{5} [/tex]
And out of 2/5 surgeonfish , 3/4 are yellowtangs, that is
[tex] \frac{3}{4}* \frac{2x}{5} = \frac{6x}{20} = \frac{3x}{10} [/tex]
Required fraction is
[tex] \frac{3x/10}{x} = \frac{3}{10} [/tex]
