A and B can do a piece of work in 7 days. With the help of C they finish the work in 4 days. C alone can do that piece of work in?  Choices.
A) 33
B) 9 1/3
C) 30
D) 88
E) 11
C = 1/4 â€“ 1/7 = 3/28 =&gt; 28/3 = 9 1/3 days   Answer: 9 1/3
<result>B</result>
A and B can do a piece of work in 7 days. With the help of C they finish the work in 4 days. C alone can do that piece of work in?