Given :
10,50,80 and x are in proportion.
To Find :
The value of x.
Solution :
It is given that 10,50,80 and x are in proportion.
It means that 10,50 and 80, x are same ratio.
[tex]R = \dfrac{10}{50}=\dfrac{80}{x}\\\\x = 400[/tex]
Therefore, the value of x is 100.