My calculator won't solve...

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I have two concerns about solving a binomial distribution question...

1. I need to solve



But when I type in the correct solve command my calculator spouts out exactly this:



This is obviously of no use to me...

The only way I can solve this is to solve and then choose the direction of the inequality sign myself but this is impractical.

Please try this on your calculator. Is this supposed to happen? Can it be fixed?

2. If I solve I get two answers: n = 6.55 or n = 27.91. How can this be? The question asked for the minimum number of trials required such that . Where is this extraneous solution coming from and, moreover, which is the correct value of n?

Thanks

[Flaming_Arrow]

you cant use solve function, go to you y= screen and type the equation here and then go to XY table, if its the first question, scroll until you see a value just above 0.1 or equal to this.

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Thanks chath

[dcc]

First write out our relation: 

Which is equivalent to solving the following inequality:    (under the assumption that )

If you consider the graph of the function , clearly the x-intercepts of this function will give us the values of which you desire.

The first intercept is at , which is the the first answer you found, and this (actually 7) would be the answer to your question.

However as n increases, the effect of the term becomes more pronounced, because as ,

So as decreases, there is a second case for which gives the required probability, however since the question asked for the minimum number of trials, you can ignore this second resullt.

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Hmmm, nice way of looking at it, thanks!