There are a couple  of options.... Since cows have 4 legs and ducks 2.

4 legs = 1 cow
2 legs= 1 duck 

start with the cows and do multiples of 4, and then divide the result by two

4 x 5 (cows) = 20 (legs)
56 (total legs) - 20 =36
36/2= 18

so if you have 5 … Read more