is percentage increase and decrease equation the same + urgently need this worked out:

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I do A level biology and this frequently comes up.   Could someone also explain the answer to this?
The incidence for a type of brain cancer is 6 cases per 100 000 per year.
Use this information to calculate the expected number of volunteers in this study developing cancer during the 8.5 year period of the investigation?   Show your working.    The number of volunteers is 410 000

Please include an explanation aswell in your answer :) ?

Posted Sat 19th May, 2012 @ 20:49 by claire hopkins

2 Answers

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Equation? I though you just use the multiplier times/divided by the number you're given..

410000- (1-6/100000)^8.5x410000)= 209.05.... = 210 people (I hope that's right)

The '(1-6/100000)^8.5' bit is the multiplier for the people not getting the cancer over the 8.5 years. It's a bit like compound interest (you've probably done that at GCSE level). Multiply the answer by 410000 and you'll have the people not getting the cancer over 8.5 years out of the 410000 people.

410000 take away that will give you the number of people that will get the cancer, which is 209.05, but since we talking about people, it rounds up to 210.

That could be wrong but that's the best I can do. :P

Answered Sat 19th May, 2012 @ 21:58 by FutureMedic
Edited by FutureMedic on Sun 20th May, 2012 @ 13:38
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Not sure about your second question, but percentage increase/decrease are the same, except

% increase= (increase/original value)x100    and % decrease = (decrease/original value)x100


Answered Sun 20th May, 2012 @ 10:55 by Jess G