People and horses (legs on the ground): Infer the number of horses from total legs counted. There are as many men as horses. Half of the owners (men) are mounted; the rest walk, leading their horses. Total legs on the ground counted = 70. Find how many horses there are. Choose the correct value.

Let n = number of horses = number of men.

Count legs on the ground Men walking = n/2 ⇒ human legs on ground = (n/2) × 2 = n. All horses have 4 legs on ground regardless of riders ⇒ horse legs = 4n. Total ground legs = n + 4n = 5n = 70.

Solve 5n = 70 ⇒ n = 14.

Common pitfalls Subtracting legs for mounted horses; a mounted horse still contributes four legs on the ground.