Question

The average of six numbers is -3.65.If five numbers are each -3.20,what is the sixth number.

Answer 1

we know that the average for six numbers can be writen like:

$A=\frac{x_1+x_2+x_3+x_4+x_5+x_6}{6}$

So if 5 of them are -3.20 and the average is -3.65 we can replace that values and find the missing one:

$-3.65=\frac{5(-3.20)+x}{6}$

and we solve for x so:

$\begin{gathered} -3.65\cdot6=-16+x \\ -22+16=x \\ -6=x \end{gathered}$

So the missing value is -6