For the first 20 days, the combined rate of disappearance of pollywogs from the pond is 50+10=<<50+10=60>>60 pollywogs per day.
During these first 20 days, the total number of pollywogs removed was 60*20=<<60*20=1200>>1200 pollywogs.
This means after 20 days there were 2400-1200=<<2400-1200=1200>>1200 pollywogs left in the pond.
At a disappearance rate of rate 50 pollywogs per day, it will take an additional 1200/50=<<1200/50=24>>24 days for the rest of the pollywogs to disappear from the pond.
Thus, overall, it will take 20+24=<<20+24=44>>44 days for all of the pollywogs to disappear from the pond.
#### 44