Marlene wants to buy 12/2 = <<12/2=6>>6 shirts.
The discount price of the shirt is $50 x 20/100 = $<<50*20/100=10>>10.
So, the shirt will only costs $50 - $10 = $<<50-10=40>>40 each.
Thus, Marlene will pay $40 x 6 = $<<40*6=240>>240 for the 6 shirts.
#### 240