Question 337092
Whenever you're looking at percentage changes, you take the difference between old and new value and then divide it by the old value.
So then, the percentage change for those two days would be
{{{C=(15-12)/12=3/12}}}=25%
Positive 25% so you know the number increased.
In other words, the change from old to new value is 25% of the old value.
{{{12+(25/100)12=12+(1/4)(12)=12+3=15}}}
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As another example, if it was reversed say 15 today and 12 tomorrow. Then the percentage change would be
{{{C=(12-15)/15=-3/15}}}=-20%
Negative 20%, so you know the number decreased.
{{{15+(-20/100)(15)=15+(-1/5)(15)=15-3=12}}}
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So the percentage change going from 12 to 15 is not the same magnitude as going from 15 to 12 because it's a percentage of the starting (old) value.