Explanation:

- Let's assume the cost price (CP) for each toy is $1. So, the cost price for all toys is $100 if there are 100 toys.

- The seller sells 80% of the toys for the same amount he bought all. So, he sells 80 toys for $100.

- To find the selling price (SP) per toy, divide $100 by 80, which equals $1.25.

- Profit per toy is $1.25 (SP) - $1 (CP) = $0.25.

- Profit percentage can be calculated as:

$$\left(\frac{\text{Profit per toy}}{\text{CP per toy}}\right)\times 100=\left(\frac{0.25}{1}\right)\times 100=25\mathrm{\%}$$

- Correct Answer: Option 3 - 25%

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