Madhya Pradesh Police Exam Model Paper 8

Given:
Total observation = 10
Average of 10 observation = 30
Average of 1st 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 $=30\times 10=300$
Total sum of 1st six observation $=40\times 6=240$
Total sum of last five observation $=20\times 5=100$

6th observation is common in both 1st and last
6th observation = (Total sum of 1st six observation + Total sum of last five observation) - Total sum of 10 observation
⇒ 6th observation $=\left(240+100\right)\mathit{–}300$
$\Rightarrow 340\mathit{–}300$
$\Rightarrow 40$
∴ 6th observation is 40.