If p 5 12 and 20 are in proportion find the value of p.

Given: 

$p,\ 5,\ 12,\ 20 $ are in proportion. 

To do: 

We have to find the value of $p$.

Solution:

$\Rightarrow p:5=12:20$

$\Rightarrow p \times 20=5\times 12$    [Since, the product of the means = the product of the extremes]

$\Rightarrow 20p=60$

$\Rightarrow p=\frac{60}{20}$

$\Rightarrow p=3$