If there are 600 boys at the event, and the difference between boys and girls is 400, there are 600+400=<<600+400=1000>>1000 girls.
The total number of boys and girls at the event is 1000+600=<<1000+600=1600>>1600
60% of the total number of boys and girls at the event is 60/100*1600=<<60/100*1600=960>>960
#### 960