A can do a job in 15 days and B in 30 days. They work together for 4 days, and then A leaves. In how many more days will B finish the job?

💡 Solution & Explanation

Together they do 1/15 + 1/30 = 1/10 of the job per day, so in 4 days they finish 2/5 of it. The part left is 3/5 of the job. B alone does 1/30 of the job per day, so B needs 3/5 × 30 = 18 more days.