Cindi bought 30/0.50 = <<30/0.50=60>>60 pencils.
Marcia bought 2*60 = <<2*60=120>>120 pencils.
Donna bought 3*120 = <<3*120=360>>360 pencils.
Altogether, Donna and Marcia bought 120+360 = <<120+360=480>>480 pencils.
#### 480