70 Or 75? (Genesis 46:27 & Acts 7:14)

So how many people went down to Egypt with Jacob?  Genesis 46:27 has the number at 70 while Acts 7:14 has the number at 75.  

In Acts 14:7 Stephen is making his speech before the council and he lists the number of people as 75.  Stephen is actually quoting from the Septuagint (the Greek translation of the Old Testament or Hebrew Bible) which has the number as 75 in Genesis 46:27.  On the other hand the Masoretic text (Hebrew text) has the number as 70 in Genesis 46:27.  

A possible explanation for the two different numbers is that the Septuagint includes five additional descendants of Joseph who were born in Egypt.  The five additional people would be two sons of Manasseh, two sons of Ephraim, and a grandson of Ephraim.  

Another possible explanation for the different numbers is that 75 people went down to Egypt but five died before they met with Joseph.  The difference in the numbers would be between those who left for Egypt and those who made it to meet with Joseph.