Correct Answer - Option 1 : 10%

**Given: **

Cost price ∶ Selling price = 10 ∶ 9

**Formula Used:**

Loss = Cost Price - Selling Price

Loss% = Loss/Cost price × 100

**Calculation:**

Let assume cost price be = 10x

Selling price = 9x

⇒ Loss = 10x - 9x = x

According to the formula used

⇒ Loss% = (x/10x) ×100 = 10%

**∴ The correct option is 1 i.e.10%**