题目：有一分数序列：2/1，3/2，5/3，8/5，13/8，21/13...求出这个数列的前20项之和。
package cn.ls.lanqiao;import java.util.*;public class Test20 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();float a = 1;float b = 2;float sum = 0;float t;for (int i = 1; i <= n; i++) {sum += b / a;t = a;a = b;b = a + t;}System.out.println(sum);}
}