The mean of a sequence of n numbers is m. If we split the sequence into two sequences of lengths n1 and n2 and compute their means m1 and m2, which of the following is TRUE?
1 - m = (m1 m2) /2
2 - m = (m1 m2) / (n1 n2)
3 - m = (n2 * m1 + n1 m2) / (n1 + n2)
4 - m = (n1 ml+ n2 m2) / (n1 + n2)
???