Answer: 496 catfish
Explanation:
Let the total number of catfish in the lake be x.
The ratio of tagged catfish to the total catfish population is 124:x.
Also, few weeks later, he catches and frees 140 catfish and 35 have tags. This will be expressed as:
35:140.
Combining and expressing both ratios as fractions together will be:
35/140 = 124/x
1/4 = 124/x
x = 124 × 4
x = 496
There are 496 catfish in the lake.