Option 2 : 91.67

Given:

The average mark of six girls in the class was 90

Concept Used:

Average = Sum of observations/Number of observations

Calculation:

According to the question,

The total marks of six girls = 90 × 6

⇒ 540

Now, one of the girl's marks which were 60 was wrongly written as 50

⇒ 60 - 50 = 10

The actual marks of six girls = 540 + 10 ⇒ 550

The correct average = 550/6 ⇒ 91.67

**∴ The correct average of six girls is 91.67.**