If there were 1500 surfers on the first day, the total for the second day is 1500 surfers + 600 surfers = <<1500+600=2100>>2100 surfers
On the third day, the number of surfers was 2/5 * 1500 surfers = <<2/5*1500=600>>600 surfers
The total number of surfers at the Festival in the three days was 1500 surfers + 2100 surfers + 600 surfers = <<1500+2100+600=4200>>4200 surfers
The average number of surfers at the Beach Surf Festival for the three days is 4200 surfers / 3 days = <<4200/3=1400>>1400 surfers/day
#### 1400