In a farm there are cows and hens. If heads are counted there are 180, if legs are counted there are 420. The number of cows in the farm is :
Options:
A . 130
B . 50
C . 150
D . 30
Answer: Option D Let the number of cows be x. Then, number of hens would be (180 - x) According to the question (180 - x) × 2 + 4x = 420 ⇒ 360 - 2x + 4x = 420 ⇒ 2x = 420 - 360 = 60 ⇒ 2x = 60 ∴ x = $$\frac{{60}}{2}$$ = 30
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