Three investors own a company. One partner owns 1/4 of the company, while the second partner owns 2/5 of the company. How much does the third partner own?

We want to add these together and then subtract from one. So to add them, find a common denominator.

The closest common denominator is 20.

So convert the fractions:

5/20 and 8/20

Then add

5/20 + 8/20 = 13/20

And then subtract from 1.

1 - 13/20 = 7/20

The third partner owns 7/20 of the company.