Prep2-PS-37

请问NN:

For every integer k from 1 to 10, inclusive, the kth term of a certain sequence is given by (-1)的K+1次方乘
                2的-K次方.  If T is the sum of the first 10 terms in the sequence, then T is

答案为between 1/4 and 1/2

请问除了土法炼钢加加减减之外，还有其它思路吗? 谢谢!