I need help Manipulating an array

[flash_ee2]

I have an array declare on my main time line named W_time in it i have several numbers.
now what i want to do is add this numbers in the array together so i can have a sum, then i want to find the average for this numbers, am usint this code to find it, but it returns NaN....

for(i = 0; i < 10; i++){
sum += W_time[i];
}
myAverage = sum / 10;

does this work or is there another way to add an array. Pls help.......