Question

The average of 11 observation is 60 if the average of first five observation is 58 and that of the last five is 56, then the sixth observation is ?

• A. 85
• B. 110
• C. 90
• D. 100

Answer 1

The correct option is C 90

$\Rightarrow$ The average of $1$ observations $=60$

$\therefore$ Sum of $11$ observations $=11\times 60=660$

$\Rightarrow$ The average of first $5$ observation $=58$

$\therefore$ Sum of the first $5$ observation $=5\times 58=290$

$\Rightarrow$ The average of the last five observation $=56$

$\therefore$ Sum of the last $5$ observation $=56\times 5=280$

$\Rightarrow$ The sixth observation $=660-(290+280)$

$=660-570$

$=90$

$\therefore$ The sixth observation is $90$.