(1)7年级的众数为80, 方差为:3(80-85.5)2+(86-85.5)2+2(88-85.5)2+(99-85.5)2+(74-85.5)2+(91-85.5)2+(89-85.5)2 | 10 | =46.05; 8年级的中位数为86, 方差=[(85-85.5)2+(85-85.5)2+(87-85.5)2+(97-85.5)2+(85-85.5)2+(76-85.5)2+(88-85.5)2+(77-85.5)2+(87-85.5)2+(88-85.5)2]÷10=3(80-85.5)2+(86-85.5)2+2(88-85.5)2+(99-85.5)2+(74-85.5)2+(91-85.5)2+(89-85.5)2 | 10 | =31.25; 9年级的平均数=82+80+78+78+81+96+97+88+89+86 | 10 | =85.5, 众数=78, 方差=[(82-85.5)2+(80-85.5)2+(78-85.5)2+(78-85.5)2+(81-85.5)2+(96-85.5)2+(97-85.5)2+(88-85.5)2+(89-85.5)2+(86-85.5)2]÷10=43.65.
(2)因为三个年级的平均数都相同,并且8年级方差最小,因此8年级实力更强. |