Question

Rylan is testing 2 different types of nail polish on her fingernails to determine which one lasts longer. She purchases Brand A and Brand B from the drug store. She then paints her nails with Brand A and her sister's nails with Brand B. She compares the nail polish at the end of the week and determines that Brand B lasts longer because there are fewer chips than Brand A. Why is her conclusion not valid?
She painted her sister's nails with Brand A, not her own nails.
She painted her sister's nails with Brand B, not her own nails.
She did not say how much each polish chipped by the end of the week.
She purchased 2 different types of nail polish.

Answer 1

B is the answer and also they did not do the exact same things and her sister might not have liked it and tried to get it off

Answer 2

Her conclusion is not valid because she painted her sister's nails with Brand B, not her own nails.

Rylan and her sisters might have participated in different activities that may factor in the speed or occurrence of nail chips.

Had Rylan applied both brands on her nails, like brand A to her right hand nails and Brand B to her left hand nails, she would have drawn valid conclusions based on her primary observations.