A bakery baked 40 loaves on Friday at an average weight of 450 g, 60 loaves on Saturday at an average weight of 480 g and 100 loaves on Sunday at an average weight of 510 g. What was the average weight of all the loaves baked over the three days?

Total weight = $40\times 450+60\times 480+100\times 510=18000+28800+51000=97,800$ g over 200 loaves, so the average is 97800/200 = 489 g. 480 g is the plain average of 450, 480 and 510, which ignores that Sunday alone supplied half the loaves. 471 g attaches the counts to the wrong days (100 loaves at 450 g and 40 at 510 g). 490 g reads the counts 40, 60 and 100 as 1 : 2 : 3, but they are 2 : 3 : 5.