In collection of animals including birds and beasts they had 43 heads and 120 feets. How many birds and beasts are there in collection?

Birds and beasts have one head each. So totally there are 43 birds & beasts.

Let number of birds = x

number of beasts = (43-x)

Birds have 2 feet and beasts have 4 feet.

Total feet = 2 * no of birds + 4 * no of beasts

= 2 * x + 4 * (43 -x)

= 172 - 2*x (on simplification)

= 120 (given)

172 - 2*x = 120

2*x = 172 - 120 = 52

x = 52/2 = 26

number of birds = x = 26

number of beasts = 43 -x = 43 -26 = 17

(check: 26 + 17 = 43 ; 26*2 + 17*4 = 52 + 68 = 120)