First, let's get a common denominator in the two fractions that we are given.
[tex] \frac{1}{4} = \frac{5}{20} [/tex]
[tex] \frac{2}{5} = \frac{8}{20} [/tex]
Add the two and you get [tex] \frac{13}{20} [/tex]
Therefore, [tex] \frac{7}{20} [/tex] is remaining and that is how much the third partner owns.