AMC 8 1988 Problem 19

AMC8 1988 年第 19 题

数列与规律★★★☆☆

What is the

100\text{th}

number in the arithmetic sequence: 1,5,9,13,17,21,25,... ?

等差数列 1,5,9,13,17,21,25,... 中的第 100 个数是多少？

正确答案 · Correct Answer

解析 · Solution

Solution 1

The common difference of this arithmetic sequence is 5 - 1 = 4. From the first term, it takes 99 steps to reach the

100\text{th}

term, so the

100\text{th}

term is

1 + 4\cdot99 = 397

继续练习