Percent of Change anyone!?!?

Question

I have to find the percent of decrease for 21 to 11.5, 25 to 15, 190cm to 52cm, 34m to 31.7m, The % of increase 4: 75 to 110, 15 to 95, 7h to 8.5h, 1.35km to 4.9 km, 2ft to 5ft 8in, 9mm to 18cm

THNX

Answer 1

Here are basic equations that you can use.

N - first value
n - second value


percent decrease = [(N-n)/N]*100%

*basically take the difference of the two values and solve the percentage value of the decrease compared to its initial value.
ie: [(21-11.5)/21]*100% = .452*100% = 45.2% decrease


percent increase = [(n/N)*100%]-100%

*n/N*100% gives you the percent value of the second in comparison to the first value, then you have to subtract its initial value worth (which is 100%) to solve for the overall increase
ie:[(110/75)*100%] -100% = [1.46*100%] -100% = 146% - 100% = 46% increase

Answer 2

You write the actual amount of the decrease (or increase) over the original amount = p over 100, then cross multiply and divide to get p the percent. Example

21 went down to 11.5, a decrease of (21-11.5) = 9.5

So 9.5/21 = p/100
21p = 950

p = 950/21 = 45.2 % decrease