Question 323212
First assign variables.  B/c both the cats and fish are compared to mice,
let MICE = x
"3 times as many fish as mice"
let FISH = 3x
"half as many cats as mice"
let CATS = 1/2x

So add all three and set equal to the total pets
{{{x+3x+(1/2)x=36}}}
solve for x
{{{4x+(1/2)x=36}}}
{{{(8/2)x+(1/2)x=36}}}
{{{(2/9)*(9/2)x=36*(2/9)}}}
{{{x=(72/9)}}} or 8

   x = 8 MICE
  3x = 24 FISH
1/2x = 4 CATS

*check*
{{{8+24+4=36}}}
{{{36=36}}}