X can finish a work in 30 days. Y can finish the same work in 15 days. Yworked for 10 days and left the job. how many days does X alone need to finish the remaining work? Choose the correct choice:
A) 3
B) 10
C) 6
D) 8
E) 9

Rationale: "work done by x in 1 day = 1 / 30 work done by y in 1 day = 1 / 15 work done by y in 10 days = 10 / 15 = 2 / 3 remaining work = 1 – 2 / 3 = 1 / 3 number of days in which x can finish the remaining work = ( 1 / 3 ) / ( 1 / 30 ) = 10 b"
Answer: B