Answer: 25%
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Work Shown:
A = old value = 12 pounds
B = new value = 15 pounds
C = percent change
C = [ (B-A)/A ] * 100%
C = [ (15-12)/12 ] * 100%
C = (3/12)*100%
C = 0.25*100%
C = 25%
The positive C value indicates a percent increase
So effectively, we find the difference or change in weight (B-A) and divide it over the original weight (A). That leads to 0.25 which converts to 25%
Note that,
25% of 12 = 0.25*12 = 3
This says that the puppy gained 3 pounds, which is the value of B-A
Since the puppy gained 3 pounds, the new weight is 12+3 = 15 pounds
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As an alternative, we could divide the two values B over A to find that
B/A = 15/12 = 1.25
Then subtract 1 from this result: 1.25 - 1 = 0.25 = 25%