Acts 7:14 states that "Joseph sent word and invited Jacob his father and all his relatives to come to him, seventy-five persons in all." This seems to contradict Deut. 10:22, Ex. 1:5; and Gen. 46:27 which all say it was 70 persons. What accounts for this difference?
Acts 7:14 is part of a speech which Luke records. The speech is given by Stephen, a Greek Jew who no doubt would have read the Septuagint. The Septuagint (along with the Dead Sea Scrolls) varies from the Masoretic Text in both Genesis 46:27 and Exodus 1:5 and reads instead "75 people." It's likely Stephen was quoting this tradition.