maths. 一問

(a + b + c) / 3 = 80 2/3 ------ (1)
(a + b) / 2 = 82 ------ (2)
(b + c) / 2 = 81 ------ (3)

from (1),
(a + b + c) / 3 = 80 2/3
a + b + c = 242 ------ (4)

from (2),
(a + b) / 2 = 82
a + b = 164 ------ (5)

from (3),
(b + c) / 2 = 81
b + c = 162 ------ (6)

(4) - (5),
(a + b + c) - (a + b) = 242 - 164
c = 78

(4) - (6),
(a + b + c) - (b + c) = 242 - 162
a = 80

sub (c = 78) and (a =80), from (4),
80 + b + 78 = 242
b = 242 - 80 - 78
b = 84

The answer is a = 80, b = 84, c = 78

1)anw:b=41