Correct Answer - Option 1 : 40.8

**Given:**

Average of 13 numbers = 42

Average of first 7 numbers = 38

Average of last 7 numbers = 48

**Formula used:**

Average = sum of observations/total number of observations

**Calculation:**

Sum of 13 numbers = 13 × 42 = 546

Sum of first 7 numbers = 7 × 38 = 266

Sum of last 7 numbers = 7 × 48 = 336

7^{th} number = 266 + 336 - 546 = 56

Required average = (546 - 56)/12 ≈ 40.8

**∴ The average is 40.8**