In a farmer's house, there are Chickens and goats. The total number of their heads is 42 and the total number of their legs is 138. Find the number of Chickens.

Correct option is C

​Given:

Total heads = 42

Total legs = 138

Solution:

Let chickens = x
, goats = y
:

​$$x + y = 42$$ ... (1)

​$$2x + 4y = 138$$.....(2)

From equation(1);

$$x + y = 42$$​

$y=42-x$

Substitute value of y into $$2x + 4y = 138$$:

​$$2x + 4(42 - x) = 138 \\ \ \\ 2x + 168 - 4x = 138 \\ \ \\ 2x - 4x = 138 -168$$​​

​$$−2x=−30 \\ \ \\   x=15$$ 

Thus, the number of chickens is 15