② The average mass of tagged fish is184 ÷100 =1.84 kg.
The mass of 20 marked fish is 1.84× 20 = 36.8kg,
The average mass of fish is (184+416-36.8) ∴ (100+200-20) ≈ 2.011kg.
That is1000× 2.011= 2011kg.
Answer: Wang Laohan's fish pond is estimated to have 1000 fish, and the total mass is estimated to be 20 1 1 kg.