Find r in P(7, r) Recall the permutations formula: 7! / (7-r!) = 840. We run 7! through our search engine and we get: 7! = 5040 5040 / (7 - r)! = 840 Cross multiply, and we get: 5040/840 = 7 - r! 6 = (7 - r)! Since 6 = 3*2*! = 3!, we have; 3! = (7 - r)! 3 = 7 - r To solve for r, we type this equation into our search engine and we get: r = 4
