#include <stdio.h>
 
int main() {
    int n;
    int q;
    int data[50005];
    scanf("%d %d", &n, &q);
 
    for (int i = 1; i <= n; i++) {
        scanf("%d", &data[i]);
    }
 
    for (int i = 0; i < q; i++) {
        int a, b;
        double total = 0;
 
        scanf("%d %d", &a, &b);
 
        for (int j = a; j <= b; j++) {
            total = total + data[j];
        }
 
        int jumlah_hari = b - a + 1;
        double rata = total / jumlah_hari;
 
        printf("Hari ke %d-%d: %.2f\n", a, b, rata);
    }
 
    return 0;
}

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10 4
10 20 30 40 50 0 0 0 0 0 
1 1
1 5
2 4
1 10