数学OG 189题 PS

Yilan_asg

                                                                                                                                                [size=15.000000pt]For any positive integer [size=15.000000pt]n[size=15.000000pt], the sum of the first [size=15.000000pt]n [size=15.000000pt]positive integers equals n（n+1）/2. Whatis the sum of all the even integers between 99 and 301?
                                        [size=15.000000pt](A) 10,100(B) 20,200(C) 22,650(D) 40,200(E) 45,150
[size=15.000000pt]这道题解了半天都得不到B的结果，解析说The sum of the even integersbetween 99 and 301 is the sum of the even integers from 100 through 300, or thesum of the 50th even integer through the 150th even integer. To get this sum, findthe sum of the first 150 even integers and subtract the sum of the first 49 evenintegers.
                                                                                                                                                [size=15.000000pt] 怎么又转换到50到150的偶数求和了。。。

[size=15.000000pt]

[size=15.000000pt]求问大神们，谢谢！
                               
                       
               
                               
                       
               

Fiona09

LZ重新排个版，相信大神们会愿意回答的