PTA は生徒に平均点と優秀率の回答を求めます

#include<stdio.h>
int main( )
{
    int n,i,grade;
    double sum=0,average,rate,count=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&grade);
        if(grade>=90)
            count++;
        sum+=grade;
    }
    average=sum/(n*1.0);
    rate=(count*1.0)/(n*1.0);
    printf("average=%.2lf\nrate=%.2lf",average,rate);
    return 0;
}