单选题
The pages of a report are numbered consecutively from 1 to 10. If the sum of the page numbers up to and including page number z of the report is equal to one more than the sum of the page numbers following page number x, then x=
【正确答案】
D
【答案解析】[解析] 设前x页的和为m，则x页之后的几页的和等于m-1，根据题意可得：
2m-1=1+2+3+…+10=55
→m=28
由此考生可推出x=7。
考生也可用等差数列前n项的求和公式
2m-1=1+2+3+…+10=55
→m=28
由此考生可推出x=7。
考生也可用等差数列前n项的求和公式