Matt and Peter can do together a piece of work in 20 days. After they have worked together for 10 days Matt stops and Peter completes the remaining work in 10 days. In how many days Peter complete the work separately.
Choose the correct answer.
A) 21 B) 20 C) 22 D) 23 E) 24

Rationale: "together they complete the job in 20 days means they complete 10 / 20 of the job after 10 days . peter completes the remaining ( 10 / 20 ) of the job in 10 days which means that the whole job ( 1 ) can be completed in x days . < = > 8 / 20 - > 10 < = > x = 10 / ( 10 / 20 ) = 20 b"
Answer: B