Help with percentages question? (1 Viewer)

[ellie_bubs]

Hey everyone, i am doing questions from the 2002 paper and came across one which is annoying the hell out of me but is probably so simple.
It's question no. 19 in the m/c;
In one year, the population of a city increased by 20%. The next year, it decreased by 10%.
What was the percentage increase in the population over the two years?
a) 8%
b)10%
c)15%
d)30%
The answer is actually 8% and i have no idea how they got it, i just did it the simple way and supposed it was a 10% increase but this is obviously wrong
I would really appreciate any help with this its annoying the crap out of me!
Thanx guys

 

[ellie_bubs]

Thanx heaps for that, i think ill go by the second formula
Good luck with the exams

 

[PC]

Or a really quick way ...

An increase of 20% can be done by multiplying by 1.20
A decrease of 10% can be done by multiplying by 0.90

So ... 1.20 x 0.90 = 1.08

The 1.08 represents an increase of 8%.

 

[Kimmi_R]

yeah. remember when anything is decreasing by a percent, or you have to find the original price of something before inflation add 1 and divide eg decreasing by 15. divide by 1.15