The original amount is $50 so half is $50/2 = $<<50/2=25>>25
4 students paid half ($25) for a total of 4*$25 = $<<4*25=100>>100
There are 25-4 = <<25-4=21>>21 students left
21 students paid the full amount ($50) for a total of 21*$50 = $<<21*50=1050>>1050
They were able to gather a total of $100+$1050 = $<<100+1050=1150>>1150
#### 1150