in a group of cows and hens , the number of legs are 20 more than twice the number of heads . the number of cows is :
"let no of cows be x , no of hens be y . so heads = x + y legs = 4 x + 2 y now , 4 x + 2 y = 2 ( x + y ) + 20 2 x = 20 x = 10 . answer : d"
subtract(20, const_4)