6+8+ 15+x+y+2 = 40 4×6+5×8+6× 15+7x+8y+50×2 = 320
The solution is x=6 y=3.
A: Six people donated seven volumes and three people donated eight volumes.
(2) The average number of books donated is 320÷40=8,
The 20th, 2nd1numbers are all 6, so the median is 6.
The most common occurrence is 6, so the mode is 6.
Because the average of 8 is greatly influenced by two fifties, the average can't reflect the general situation of the number of books donated by students in this class.