Hi cookiepie,
is similar to the money qn that was asked earlier. for the qn
Firstly you need to know bird has 2 legs, rabbits 4 legs... so you assume the max qty of pets goes to the birds. Hence, 12 x 2 = 24 legs
to meet the total 36 legs you need (36-24 = 12) more legs. this can only applies to the 4-legged animals.
the difference b/w rabbits and birds (4-2=2). Thus you will need 12 divide 2 = 6 rabbits
Finally, 12 pets - 6 rabbits = 6 birds.
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Another visual method, is you draw 12 circles which represents 12 animals. then you draw 2 sticks (as legs) on each circle, and it comes to only 24 legs. then ask you girl to draw 2 more sticks on the exisiting circles that will results in 36 legs in total, meaning you need to draw on 6 circles only because 12 more legs required. from the picture you will be able to count how circles having 2 sticks only, which represent the birds.
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Hope my explanation helps.