A & B working together can do a job in 30 days. They worked only for 20 days and the rest job is done by A in next 20 days. In how many days A can do the complete job individually?

Sure, let's solve this step by step:

Step 1: A & B together can do a job in 30 days. So, the combined rate of A & B is 1 job/30 days = 1/30 of the job per day.

Step 2: They worked together for 20 days, so they completed 20 * (1/30) = 2/3 of the job.

Step 3: The rest of the job, which is 1 - 2/3 = 1/3 of the job, is done by A alone in 20 days. So, the rate of A is 1/3 job/20 days = 1/60 of the job per day.

Step 4: Therefore, A can do the complete job individually in 1 job / (1/60 job per day) = 60 days.