4. A household raises chickens and rabbits. The chickens and rabbits have a total of 50 heads and 140 legs. How many chickens and how many rabbits are there in this household?
First method:

If all 50 were chickens, then the number of legs would be $50 \cdot 2=100$. 2 POINTS

Since the number of legs is $140-100=40$ more and since $40: 2=20, \quad 2$ POINTS

there are 20 rabbits in the household. 1 POINT

So, the number of chickens is $50-20=30$. 1 POINT

TOTAL 6 POINTS