The number of cars in the back parking lot was 100*2 = <<100*2=200>>200 times more than those in the front parking lot.
There were 200+100 = <<200+100=300>>300 cars in the back parking lot.
A total of 300+100 = <<300+100=400>>400 cars were present before the play began
The total number of cars that parked in the theater during the play is 700-400 = <<700-400=300>>300 cars
#### 300