Question

A store marks up an item from $50 to $100.

Answer 1

A) it is a 100% increase 

B) 200% of $50

Answer 2

A.) Half of 100 is 50. So that means that the percentage increase is 50%.
b.) Same as a, 
100%/x% = 100/50
(100/x)*x = (100/50)*x Multiply both sides by x
100 = 2*x
100/2 = x
50 = x
x= 50