For those that are to be redeemed — 'Tis probable, in the exchange they began with the eldest of the first — born, and so downwards, so that those were to be redeemed, who were the two hundred, seventy three youngest of them.
Related Commentaries of Numbers 3:46
Numbers 3:46
46 And for those that are to be redeemed of the two hundred and threescore and thirteen of the firstborn of the children of Israel, which are more than the Levites;