Correct Answer - Option 3 : 20%

**Given:**

The price of two books A and B is 3500 and 4400 respectively.

The price of A decreases by a certain %.

The price of B increased by the same percentage.

The ratio of A and B after this change is 35: 66.

**Formula used:**

Profit or Gain = Selling price – Cost Price

Loss = Cost Price – Selling Price

Profit percentage = (Profit/Cost Price) × 100

Loss percentage = (Loss/Cost price) × 100

**Calculation:**

Let x be the % with which A decrease and B increases.

ATQ,

{3500(100 – x)}/{4400(100 + x)} = 35/66

⇒ (100 – x)/(200 + 2x) = 1/3

⇒ x = 20

**∴ Required percentage is 20%**