The 5% discount amounts to $50 x 5/100 = $<<50*5/100=2.50>>2.50.
So the total discount given to the customer for 4 months was $2.50 x 4 = $<<2.5*4=10>>10.
The customer was supposed to pay $50 x 4 = $<<50*4=200>>200 in all for 4 months without discount.
Since the customer is entitled to the discount, then he only paid a total of $200 - $10 = $<<200-10=190>>190 for 4 months.
#### 190