The original price of a T shirt was $20. At a sale, it was sold at a 20 percent discount. Nathania paid $128 for some of these T shirts. How many T shirts did she buy?
Let's say that Nathania bought x T-shirts.
If the original price of each T-shirt was $20, the discount on each T-shirt was 20/100*$20 = $<<20/100*20=4>>4
The price of each T-shirt after the discount was $20-$4 = $<<20-4=16>>16.
If Nathania bought x T-shirts at $16 each, she paid $16*x = $128
The number of T-shirts Nathania bought is x = $128/$16 = <<128/16=8>>8 T-shirts. Answer: \boxed{8}.