Question

The mean of $10$ numbers is $12.5,$ the mean of first six numbers is $15$ and mean of last five is $10,$ then sixth number is

• A. $15$
• B. $12$
• C. $18$
• D. $12.5$

Answer 1

Answer: (A)

Let numbers be $a_1,a_2,...,a_{10}\cdot \sum _{i=1}^{10}{a}_i=125,\sum _{i=1}^6{a}_i=90,\sum _{i=6}^{10}{a}_i=50$
$\therefore a_6+125=90+50\therefore a_6=15$