GWD21-5(no found among old discussions)

If N=1/3 + 1/3^2 + 1/3^3, then N is between

a) 0 and 1/9

b) 1/9 and 1/3

c) 1/3 and 8/9

d) 8/9 and 4/3

e) 4/3 and 2

key is C.

chose the closed one?

其实只要看1/3+正数>1/3

另外两个小于1/3,所以小于1,没必要小于4/3.

所以C