40-25= 15 (only)

After subtracting 50, chickens and rabbits have the same number of legs, and each rabbit has twice as many legs as each chicken, so the number of chickens in the remaining number is twice that of rabbits.

Number of rabbits: 15/( 1+2)=5 (only)

5*2= 10 (only)

Chicken: 25+ 10=35 (only)

It can also be assumed that if 50 rabbits are added and the number of legs of chickens and rabbits is the same, then if 50/4= 12.5 rabbits are added, the total number of chickens and rabbits will become 40+ 12.5=52.5.

The number of legs is the same, but the number of legs of each rabbit is twice that of each chicken, so the number of chickens in 52.5 is twice that of rabbits.

There are 52.5 rabbits at this time /( 1+2) = 17.5 rabbits.

Original rabbit: 17.5- 12.5=5.

Chicken: 40-5=35.