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I want solve this probability: For $p= 0.4$ $q=0.8$ $n= 20$

$1-P(5<x<11)$

=

$1-\sum_{k=6}^{10} \binom{20}{k}(0.4)^k(0.6)^{20-k}. Wolfram Alpha -> = 0,2531$

Is calculation method right?

And is there a way to solve this in a hand calculator e.g. CASIO fx-991ES?

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Subtract the value of your sum from 1, as you indicated above. Also, check your $q$ value... (I changed your first equation to what I thought you wanted.) –  David Mitra Nov 15 '11 at 21:55
    
That formula involves nothing more complicated than addition, subtraction, multiplication, and division, so if your calculator can do the four arithmetic operations, it ought to be able to evaluate that sum. –  Gerry Myerson Nov 15 '11 at 22:08
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