A can do a piece of work in 4 days. B can do it in 5 days. With the assistance of C they completed the work in 2 days. Find in how many days can C alone do it? Choose the correct option:
A) 23 days B) 18 days C) 20 days D) 22 days E) 28 days
20 days   20 days   20 days = 1/2 - 1/4 - 1/5 = 1/20 =&gt; 20 days
<result>C</result>
A can do a piece of work in 4 days. B can do it in 5 days. With the assistance of C they completed the work in 2 days. Find in how many days can C alone do it?