Answer:
a: The percentage change from 1/3 to 2/3 is 100 % 
b: The percentage change from 1/3 to 1/6 is 0 % 
Explanation:
use this formula: 
 ((y2 - y1) / y1)*100 = your percentage change 
(where y1=start value and y2=end value) 
 
((2/3 - 1/3) / 1/3) * 100 = 100 %
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((y2 - y1) / y1)*100 = your percentage change 
(where y1=start value and y2=end value) 
 
((1/6 - 1/3) / 1/3) * 100 = 0 %