The number of Levites in Numbers 1-3 adds up to 22,300, but the Bible says 22,000. The missing 300 are the firstborn of the Levites. They weren't counted because they already belonged to God.
Read the census carefully and compare the number of firstborn males in each of the tribes of Israel to the number of people in each tribe. How many children must each family have had to make these numbers work? Even considering that many firstborn men died in Egypt from disease, hard labor, or disobedience to the instructions of Passover, the ratio is still astonishing.