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Statistics for Decision- Making in Business - Maricopa Community ...

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So, we had 10 trials and wanted to know the number if ways <strong>in</strong> which 9 heads (successes) can be<br />

<strong>in</strong>cluded <strong>in</strong> the mix. We have:<br />

. /<br />

Then, we simply need to f<strong>in</strong>d the probability of just one of those arrangements and multiply it by<br />

the number of different arrangements.<br />

S<strong>in</strong>ce we def<strong>in</strong>ed a head result<strong>in</strong>g as a success, then, what we just calculated was:<br />

. / ( ) ( )<br />

At first glance, it might seem a little confus<strong>in</strong>g that the second exponent is the number of trials<br />

less the number of successes.<br />

Why is this<br />

Suppose there are 10 trials and you want 6 successes. This necessarily means that the other 4<br />

trials would result <strong>in</strong> failures. This is precisely , or the number of trials less the<br />

number of successes.<br />

Let‟s make this <strong>for</strong>mula easier to consider. First off, let‟s def<strong>in</strong>e some variables:<br />

Let<br />

Now, <strong>in</strong> any event, success and failure make up the whole sample space. That is:<br />

S<strong>in</strong>ce they make up the sample space,<br />

So,<br />

( ) ( )<br />

<strong>Statistics</strong> <strong>for</strong> <strong>Decision</strong>-<strong>Mak<strong>in</strong>g</strong> <strong>in</strong> Bus<strong>in</strong>ess © Milos Podmanik Page 149

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