Question 934853
q, original number of fish.



{{{q-(2/3)q}}} first give-away.
{{{q-(2/3)q-(3/5)(q-(2/3)q)=30}}}, the second give-away.



{{{q-(2/3)q-(3/5)q+(3/5)(2/3)(q)=30}}}


{{{q-(2/3)q-(3/5)q+(2/5)q=30}}}


{{{(1-2/3-3/5+2/5)q=30}}}


LCD is {{{3*5}}}, so multiply left and right by this.


{{{(15-10-9+6)q=30*15}}}


{{{(5-9+6)q=30*15}}}


{{{2q=30*15}}}


{{{q=15*15}}}


{{{highlight(q=225)}}}



Mistakes are easily made in this solution.  Watch signs and factors carefully.