12, 17, x, 25, 8

А)

(12 + 17 + x + 25 + 8) : 5 = 78

12,4 + x/5 = 78

x/5 = 65,6

x = 328

Б)

(12 + 17 + x + 25 + 8) : 5 = 31

12,4 + x/5 = 31

x/5 = 18,6

x = 93

В)

(12 + 17 + x + 25 + 8) : 5 = 62

12,4 + x/5 = 62

x/5 = 49,6

x = 248

Г)

(12 + 17 + x + 25 + 8) : 5 = 18

12,4 + x/5 = 18

x/5 = 5,6

x = 28