真心求助og DS133

Karmalotse

133. Are all of the numbers in a certain list of 15 numbers
equal?
(1) The sum of all the numbers in the list is 60.
(2) The sum of any 3 numbers in the list is 12.
答案选B，可是og上的解释看不太懂，有简单一点的证明方法吗？先谢过各位！

Karmalotse

thank you

haze619

条件（2）a1+a2+a3=a2+a3+a4，所以a1=a4，多算几次就有

a1=a2=a3=a4=...=a15

所以，选B