Solution: (10× 4-10) ÷ (3-1) =15 (year)
A: When Xiao Ming 15 years old, his father was three times as old as Xiao Ming.
(2) Analysis: Because ducks have two legs and cows have four legs. Suppose all ducks, a * * * has 20×2=40 legs, and lacks 56-40- 16 legs. Because cows are treated as ducks, they will lose 16 legs. Each cow is regarded as a duck, and it will lose 4-2=2 legs, so the cow has 65438+.
Answer: (56-20×2)÷(4-2)=8 (only)
20-8= 12 (only)
Answer: There are 8 cows, 12 ducks.
Thinking: Suppose all cows are?