Danestress Posted June 1, 2009 Share Posted June 1, 2009 I am a bit confused. My math lesson (BJU 6th grade math, lesson 138, for those who want to know) has me the following information to teach probability: Say you gave 20 people a scrap of paper and had them write a number between 1 and 10. There is a chart showing how many people picked each number. For example, 4 out of the 20 wrote the number "7." So the book goes on to show that out of 20 possible answers, seven was picked 4 times, so the probability of picking 7 is 4/20 or 1/5 or 20%. Except that's not right, right? The probability of picking any number is probably the same as a any other right? So really it would be more like 10% right? Or maybe studies who that's not true - that people rarely pick 1 or 10 (let's say) and 7 is therefore slightly more likely to be picked. But either way, a survey of 20 people will hardly be accurate. I hate when I am supposed to teach things that just don't seem right to me! Quote Link to comment Share on other sites More sharing options...

Carrie12345 Posted June 1, 2009 Share Posted June 1, 2009 I am a bit confused. My math lesson (BJU 6th grade math, lesson 138, for those who want to know) has me the following information to teach probability: Say you gave 20 people a scrap of paper and had them write a number between 1 and 10. There is a chart showing how many people picked each number. For example, 4 out of the 20 wrote the number "7." So the book goes on to show that out of 20 possible answers, seven was picked 4 times, so the probability of picking 7 is 4/20 or 1/5 or 20%. Except that's not right, right? The probability of picking any number is probably the same as a any other right? So really it would be more like 10% right? Or maybe studies who that's not true - that people rarely pick 1 or 10 (let's say) and 7 is therefore slightly more likely to be picked. But either way, a survey of 20 people will hardly be accurate. I hate when I am supposed to teach things that just don't seem right to me! In the example, you know for a fact that 4 people wrote 7 and 16 people did NOT write 7. The odds are, indeed, 4/20. But throwing in the option of *chosing which number to write does muck things up a whole bunch for me. For the record, there won't ever be 20 options when the parameters are numbers 1-10. The maximum amount of options would be 10. ETA: Ds is doing probability now and I HATE IT! Quote Link to comment Share on other sites More sharing options...

Jacquelyn in NC Posted June 1, 2009 Share Posted June 1, 2009 The probability of an individual person picking 7 is one chance in ten, or 10%. Even though 4 people picked 7 in this problem, which is higher than you might expect, if you repeated the experiment often enough the average number of people to pick 7 would approach 1 person in 10. There may be a second (implied) part to this problem, though. If you took the answers of all 20 people and put them in a hat and picked one, the chances of picking a 7 from THAT pool is indeed 4/20, or 20%. HTH. Quote Link to comment Share on other sites More sharing options...

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