Problem

Source:

Tags: algebra, inequalities



For the real numbers $a, b, c, d$, the following inequalities hold: $$a + b + c \le 3d, \,\,\, b + c + d \le 3a, \,\,\,c + d + a \le 3b, \,\,\,d + a + b\le 3c.$$Compare the numbers $a, b, c, d$.