Arun can complete a survey on his own in 30 days, and Bipin is 50% more efficient than Arun. Both begin the survey together, but Arun stops after 6 days. How many more days does Bipin need to finish it?

Take the survey as 60 units: Arun does 2 units a day and Bipin, being half as productive again, does 3. Six days together give 30 units, leaving 30, which Bipin clears at 3 a day in 10 more days. 15 days finishes the remainder at Arun's 2 units a day. 16 days is the total time (6 + 10), not the further days asked for. 6 days assumes both keep working (60 ÷ 5 = 12 days in all), which contradicts Arun stopping.