Answer:
7/20
Explanation:
Use a common denominator (in this case it is 20)
Multiply 1/4 by 5 to get 5/20
Multiply 2/5 by 4 ro get 8/20
5/20 + 8/20 = 13/20 (Combined shares of the 1st and 2nd partner)
subtract 13/20 from 20/20 ro find the remaining share of the company
the last partner owns 7/20 of the company
:)