If $6,\ x,\ 8,\ 8 $ are in proportion. Find the value of $x$.

Given: 

$6,\ x,\ 8,\ 8 $ are in proportion. 

To do: 

We have to find the value of $x$.

Solution:

$\Rightarrow 6:x=8:8$

$\Rightarrow 8\times {x}=8\times {6}$    [Since, the product of the means = the product of the extremes]

$\Rightarrow 8x=48$

$\Rightarrow x=\frac {48}{8}$

$\Rightarrow x=6$