There are $$20$$ chickens and rabbits in the case, and the total number of legs is $$48$$. How many rabbits in this case? 
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If all were rabbits,  $20\times 4= 80$  the total number of legs would be $$$80$$.  $80- 48=32$  The difference is $$$32$$.  $4-2=2$  $32\div 2=16$  $20-16=4$ 