Question

The average of 15 observations is 26. If the average of the first 8 observations is 22 and that of the last 8 observations is 29. Find the 8^th observation.
1. 16
2. 18
3. 28
4. 26

Answer 1

Correct Answer - Option 2 : 18

Given∶

Average of 15 observations = 26

Average of first 8 observations = 22

Average of last 8 observations = 29

Formula Used∶

Sum of observations = Average × Number of Observations

Calculation∶

Average of first 8 observations = 22

Sum of first 8 observations = 22 × 8 = 176

Average of last 8 observations = 29

Sum of last 8 observations = 29 × 8 = 232

Now, average of 15 observations = 26

Sum of 15 observations = 26 × 15 = 390

∴ The 8^th observation = (176 + 232) – 390 = 408 – 390 = 18

∴ 18 is the 8^th observation.