Old Testament readings use the Septuagint , the Scripture the apostles quoted. Masoretic numbering shown for reference.Learn why
LXX

Judges 20:31

And the children of Benjamin went out to meet the people, and were all drawn out of the city, and began to smite and slay the people as before in the roads, whereof one goes up to Bæthel, and one to Gabaa in the field, about thirty men of Israel.

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