Im getting "division by zero" error in python and I dont have a clue why : I dont know why but, python says that ```( (x1[0]*(len(x1)-1)) + (x2[0]*(len(x2)-1)) + (x3[0]*(len(x3)-1)))``` equals 0, which shouldnt in my opinion. I've tested that code, separately, without it being a divisor, and it didnt output 0 value.
```
def av(x):
    c = 0
    alist = x
    alist.pop(0)
    for a in alist:
        c += a*x[0]
    return c
average = lambda x1,x2,x3: (av(x1) + av(x2) + av(x3))/( (x1[0]*(len(x1)-1)) + (x2[0]*(len(x2)-1)) + (x3[0]*(len(x3)-1)))
print(average([0,0],[1,4],[1,5]))```