In a farm, 40% of the birds are chickens. If 20% of the chickens are sold, by what percentage has the total number of birds decreased?

1. Problem Description

In a farm, 40% of the birds are chickens. If 20% of the chickens are sold, by what percentage has the total number of birds decreased?

2. Solution Steps

Let the total number of birds be $T$.

The number of chickens is $0.40T$.

The number of chickens sold is $20\%$ of the chickens, which is $0.20 \times 0.40T = 0.08T$.

The total number of birds decreased by $0.08T$.

The percentage decrease in the number of birds is

$\frac{0.08T}{T} \times 100\% = 0.08 \times 100\% = 8\%$.

3. Final Answer

The percentage decrease in the number of birds is 8%.

The answer is C) 8%.