Correct Answer - Option 2 : 400

Given:

The ratio of red and blue balls is 8 ∶ 11

The number of blue balls is 550

Calculation:

Let the number of red balls be 8x,

Then the number of blue will be 11x,

According to the question,

⇒ 11x = 550

⇒ x = 550/11

⇒ x = 50

Number of the red balls,

⇒ 8x = 8 × 50

⇒ 400

∴ The number of red balls is 400