<human>:  50% of substitute teachers walk out after 1 hour of teaching. 30% of the remainder quit before lunch. If 60 substitute teachers show up at 7 AM, how many will be left after lunch?
<bot>: How many teachers are left after half quit? ** First find the number of substitute teachers left after half quit: 60 teachers / 2 = <<60/2=30>>30 teachers
How many teachers quit after an hour? ** Then find how many teachers quit after an hour but before lunch: 30 teachers * 30% = <<30*30*.01=9>>9 teachers
How many teachers are left after lunch? ** Then subtract that number from the number of teachers left after one hour to find how many are left after lunch: 30 teachers - 9 teachers = <<30-9=21>>21 teachers
#### 21