GMAT Quantitative Section | Re: how many ways can a committee of 3 be selected from 7 so tha

Out of 7, 3 people need to be selected and arranged (into 3 different positions: President, VP, Sec)

So there are 2 ways to do it: 7 * 6* 5 (you say, select the president in 7 ways, now select VP in 6 ways and then select Sec in 5 ways) = 210

or you can use the permutation formula nPr such that nPr = n!/(n-r)!. nPr helps you select r people out of n people AND arrange those r people.
Above, we used 7P3 = 7!/(7 - 3)! = 7!/4! = 7*6*5 = 210

Now I am assuming that your question is why the formula
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