Question

The average of 10 observation is 30. The average of 1^st six observation is 40 and the average of last five observation is 20. Find the 6^th observation
1. 40
2. 38
3. 20
4. 15

Answer 1

Correct Answer - Option 1 : 40

Given:

Total observation = 10

Average of 10 observation = 30

Average of 1^st six observation = 40

Average of last five observation = 20

Formula used:

Average = Total sum/Total number

Total sum = Average × Total number

Calculation:

The average of 10 observation = 30

30 = (Total sum of 10 observation)/10

Total sum of 10 observation = 30 × 10 = 300

Total sum of 1^st six observation = 40 × 6 = 240

Total sum of last five observation = 20 × 5 = 100

6^th observation is common in both 1^st and last

6^th observation = (Total sum of 1^st six observation + Total sum of last five observation) - Total sum of 10 observation

⇒ 6^th observation = (240 + 100) – 300

⇒ 340 – 300

⇒ 40

∴ 6^th observation is 40.