My Math Forum Forecasting percentages by proportions

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 March 9th, 2014, 08:20 AM #1 Newbie   Joined: Mar 2014 Posts: 2 Thanks: 0 Forecasting percentages by proportions Is it possible to forecast a percentage using cross-multiplication? Take the following example. Say there's a garbage can into which you're attempting to throw ping-pong balls. From ten feet away, the average person makes 70%, while Jim, the class's best shooter, makes 90%. When we move the garbage can from 10' away to 7' away, the average person makes 80%. Using the proportions, what percentage X does Jim stand to make? If you plug the percentages into a proportional equation, you get: (0.9) / (0.7) = X / (0. Solving for X, you get (0.9*0./(0.7) or 1.03 (103%). Obviously not a correct answer since it's impossible to make more than 100% of one's shots. Furthermore, if you look at the equation from a standpoint of MISSES (instead of makes), the equation yields a completely different result. (0.1) / (0.3) = X / (0.2) Solving for X here, you get (0.1*0.2)/(0.3) or 0.07....which would mean Jim would shoot (1-0.067) or .933 (93.3%). So the question here is how one effectively uses ratios to forecast a percentage. Any help would be appreciated. Thanks!
 March 9th, 2014, 08:23 AM #2 Newbie   Joined: Mar 2014 Posts: 2 Thanks: 0 Re: Forecasting percentages by proportions Sorry about the smilies. The smilies were supposed to be 0.8.
 March 9th, 2014, 12:32 PM #3 Global Moderator   Joined: May 2007 Posts: 6,835 Thanks: 733 Re: Forecasting percentages by proportions Using misses makes more sense in this case. However if you went the other direction hits might be better. In either case, it is a guide only.
March 9th, 2014, 09:57 PM   #4
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Re: Forecasting percentages by proportions

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 Originally Posted by haz33 Sorry about the smilies. The smilies were supposed to be 0.8.
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