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

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Comb<strong>in</strong>ation – Order Does NOT Matter (Elim<strong>in</strong>ated)<br />

If order is to be elim<strong>in</strong>ated (<strong>in</strong> cases where order is not important), then the number of ways to<br />

select th<strong>in</strong>gs from the given is called a comb<strong>in</strong>ation and is denoted:<br />

( )<br />

NOTE: ( ) , that is, factorial is not distributable!! Subtract first, then use<br />

factorial. Additionally, the factorial of a product is not the product of factorials, that is,<br />

.<br />

For our numerator, we had selected 2 uncontam<strong>in</strong>ated bushels from a total of 18 uncontam<strong>in</strong>ated<br />

bushels, elim<strong>in</strong>at<strong>in</strong>g the number of repeats, which was 2, or . Accord<strong>in</strong>g to our new notation,<br />

this can be written as:<br />

( )<br />

And this is precisely what we have written <strong>for</strong> the numerator!<br />

For our denom<strong>in</strong>ator, we had selected 2 (general) bushels from a total of 20 (general) bushels,<br />

s<strong>in</strong>ce we want to know the total number of ways 2 objects can come out of 20, order aside.<br />

( )<br />

And this is precisely what we have written <strong>for</strong> the denom<strong>in</strong>ator!<br />

In simplified notation,<br />

( )<br />

Calculator Cl<strong>in</strong>ic – Us<strong>in</strong>g Comb<strong>in</strong>ations<br />

Follow the steps <strong>for</strong> f<strong>in</strong>d<strong>in</strong>g permutations, but <strong>in</strong> Step 3, use 3: nCr <strong>in</strong>stead.<br />

Example 2: Every week, Cori stops at Chipotle Mexican Grill <strong>for</strong><br />

lunch with his colleagues. Each time, he drops a bus<strong>in</strong>ess card <strong>in</strong>to<br />

the fishbowl <strong>for</strong> a chance to w<strong>in</strong> lunch <strong>for</strong> his entire office. After the<br />

seventh visit, Cori beg<strong>in</strong>s to wonder his chances of w<strong>in</strong>n<strong>in</strong>g. He<br />

estimates that there are approximately 40 cards <strong>in</strong> the bowl. If two<br />

were to be drawn, what is the probability Cori w<strong>in</strong>s both draws<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 125

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