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

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We f<strong>in</strong>d that there is a 62.5% chance that <strong>in</strong> a couple either the husband votes Republican, the<br />

wife votes Republican, or both vote Republican.<br />

At this po<strong>in</strong>t you might be wonder<strong>in</strong>g why we don‟t simply draw out the table and ignore the<br />

mathematical <strong>for</strong>mulas. When possible, tables are extremely useful, but they might not always be<br />

available. Consider the follow<strong>in</strong>g example.<br />

Example 3: Test<strong>in</strong>g has determ<strong>in</strong>ed that a particular ballistic missile has an<br />

80% chance of hitt<strong>in</strong>g its <strong>in</strong>tended target. Suppose that an enemy jet<br />

approaches a military base and so two missiles are fired at the <strong>in</strong>com<strong>in</strong>g jet.<br />

What is the probability that this threat is elim<strong>in</strong>ated<br />

SOLUTION: This is the probability that one or both missiles hit the target.<br />

We only have one probability, so fill<strong>in</strong>g out a table would not be possible.<br />

Let<br />

We want to know<br />

( ) ( ) ( ) ( )<br />

We already know the first two probabilities on the right hand-side (.80), but we are not given<br />

<strong>in</strong><strong>for</strong>mation on ( ). We can fairly assume that the outcome of one missile has no (or<br />

very m<strong>in</strong>imal) impact on the outcome of another missile, and so we assume the events are<br />

<strong>in</strong>dependent. This allows us to write:<br />

( ) ( ) ( )<br />

And so,<br />

( )<br />

We conclude that there is a 96% chance that the enemy jet is elim<strong>in</strong>ated.<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 104

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