JOHN and ANDREW can finish John work 30 days if they work together. They worked together for 20 days and then ANDREW left. JOHN finished the remaining work in another 20 days. In how many days JOHN alone can finish the work?  Choose the correct choice from the following.
A) 30 days  B) 60 days  C) 70 days  D) 80 days  E) 90 days
Amount of work done by JOHN and ANDREW in 1 day = 1/30   Amount of work done by JOHN and ANDREW in 20 days = 20 × (1/30) = 20/30 = 2/3   Remaining work – 1 – 2/3 = 1/3   JOHN completes 1/3 work in 20 days   Amount of work JOHN can do in 1 day = (1/3)/20 = 1/60   =&gt; JOHN can complete the work in 60 days   60 days
<result>B</result>
JOHN and ANDREW can finish John work 30 days if they work together. They worked together for 20 days and then ANDREW left. JOHN finished the remaining work in another 20 days. In how many days JOHN alone can finish the work?