Total no. of customers who came in groups = (80 + 50 + 28 + 30 + 100 + 72) = 360
Total no. of bills issued for groups of customers = (230 – 210) + (130 - 120) + (57 - 50) + (70 - 60) + (200 - 180) + (154 - 130) = 91
Therefore, Avg. no. customer in a group = 36091=4 (approx)