Question 585859
If half of the fish caught are tagged, the conservationist will estimate that about half of all the fish in the lake were tagged. And if he is the only one that's been tagging them, then half of the trout in the lake was 86 (before the fisherman started fishing). So there must have been about {{{2*86=172}}} trout in the lake. If the guy who caught them does not throw them back, now there are 20 less, for an estimate of {{{172-20=152}}} trout in the lake.