In a zoo, there are Rabbits and Pigeons. If heads are counted, there are 200 and if legs are counted, there are 580. How many pigeons are there?

Total No of 4 Leg Animal(Rabbit ) = ((Total no of legs/2) -No. of heads)
Rabbit = 580/2 - 200
Rabbit = 90
Pigeon = 200 - 90 = 110
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Alternative way:
Let rabbit =x
and Pegion =200 - x
4 x (because rabbit has 4 legs) + 2(200 - x) = 580
400 + 2x = 580
2x = 180
x = 90
Rabbit =90
Pegion=110
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Alternative way:
Let pigeons= X
Rabbits = Y
X+Y= 200 ......(1)
2X+4Y =580 .... (2)
Then
4X + 4Y = 800
2X + 4Y = 580
- - -
2X = 220
X = 110