There are numerous different ways in which commentators have sought to reconcile and understand how Joshua could assign 30,000 men to the ambush force in Joshua 8:3 and only 5,000 in Joshua 8:12.
Some suggest that the number in Joshua 8:3 refers to the entire force whereas the number in Joshua 8:12 specifies the ambush force itself.1 This is possible, although it seems clear from Joshua 8:3–4 that the figure of 30,000 refers to the men who are sent out from the main army. Perhaps there were two ambush groups set up in slightly different places. An alternative explanation is that a very early copyist erroneously changed 5,000 into 30,000.2
One thing to remember as we read these numbers is that the Hebrew word for thousand
can also refer to a military unit. That is to say, rather than 30,000 and 5,000 men being sent on ambush, we have 30 military units and 5 military units. Translating the Hebrew word in this way makes much more sense of the fact that the city of Ai only had 12,000 people.
12 He took about 5,000 men and set them in ambush between Bethel and Ai, to the west of the city.