The third proportional of 20 and 25 is:

to find: the third proportional of 20 and 25.

Third proportional, c, can be found using the formula: 

​$$c = \frac{b^2}{a}$$​​

Using the formula;

​$$c = \frac{(25)^2}{20} \\\ \\ c = \frac{625}{20} \\ c= 312.5$$​​

Thus, The third proportional of 20 and 25 is 31.25