<human>:  While playing with her friends in their school playground, Katelyn saw 50 fairies flying above the nearby forest. After about twenty minutes, one of her friends saw half as many fairies as Katelyn saw come from the east and join the fairies that were there. Ten minutes later, 30 fairies flew away. How many fairies are remaining?
<bot>: How many fairies did Katelyn's friend see? ** Katelyn's friend saw 1/2*50 = <<1/2*50=25>>25, half as many fairies as Katelyn initially saw
How many fairies are flying above the forest now? ** The total number of fairies flying above the forest now is 50 + 25 = <<50+25=75>>75
How many fairies are remaining? ** If thirty fairies then flew away, there were 75 - 30 = <<75-30=45>>45 fairies that remained.
#### 45