Collecting Design Test Data Practice Test

In the makerspace, Jamal and Sofia had a problem: books fell when carried. Design A was a flat board with no edges, and Design B had raised edges. To test both designs fairly, they put 3 books on each and walked 10 steps. They recorded the number of books that fell: A had 2 fall, B had 0 fall. Why did they test both designs the same way?

In science time, Maya and Marcus had a problem: a supply holder tipped over. Design A had a narrow base. Design B had a wide base. They tested both designs the same way by pushing gently on the side. They recorded yes/no results: A tipped (yes), B tipped (no). Why did they test both designs the same way?