f5數學 離差

平均數是10 :

(7 + 9 + 11 + 14 + 15 + 15 + x + y) / 8 = 10

x + y = 9

標準差是√89/2 :

√{(1/8)[(7-10)² + (9-10)² + (11-10)² + (14-10)² + (15-10)² + (15-10)² + (x-10)² +(y-10)²]}

= √89/2

√{(1/8)[77 + (x-10)² + (y-10)²]} = √89/2

77 + (x-10)² + (y-10)² = 178

x² + y² - 20(x + y) + 200 = 101

x² + y² - 20(9) + 200 = 101
x² + y² = 81

x² + (9 - x)² = 81

2x² - 18x + 81 = 81

x(x - 9) = 0

x = 0(rejected since x>y) or x = 9

So x = 9 , y = 0

Do you have an answer