Problem Solving

I am just beginning my GMAT prep (2nd time) and came across a problem in the princeton review cracking the GMAT book...it is on page 70...


The output of a factory was increased by 10% to keep up with rising demand. To handle the holiday rush, this new output was increased by 20%. By approximately what % would the output now have to be decreased in order to restore the original output?
a)20%
b)24%
c)30%
d)32%
e)70%


They list B 24% as the answer...I see no other answer than D32%. Am I completely missing something or is this a book mistake?

Thanks

You probably have a slight error in your calculation...

My guess is you took a number lets say 1000

10% increase 1000*1.1=1100 additional 20% increase 1100*1.2=1320

Here is your mistake 1320-1000=320...320/1000=32%

You need to take the decrease from the output after the 10 and 20% increases, not the original output

So...1320-1000=320...320/1320=24.24% round to 24%