//定义三个空数组:
var arr= [];
var sum =0
var count = []
for(var i=0 ;i<30 ; i++){
//2 4 6 8 10 12
arr.push((i+1)*2)
sum += (i+1)*2
if((i+1) % 5 == 0){
var aver = sum/5
count.push(aver)
sum = 0
}
}
console.log(count)