There is a sentence in Time magazine like this : "The Great Australian Outback Cattle Drive offers visitors a chance to ride those same desert trails, accompanying herds up to 500 strong." What does this "strong" mean?
'Strong' in this situation refers simply to the number involved. "The team was 15 strong" means the total number of available players was 15, from which the actual side of 11 would be picked. "The general attacked with an army 15,000 strong" means there were 15,000 soldiers in that particular invasion group and so on.