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# September 2002 Puzzle Solution [Preview]

If you spread your investments over 10 companies, giving each \$1.43 million, the chance that at least seven will yield 10-fold returns is more than 95 percent. If that happens, the total return would be \$100.1 million. This strategy leaves \$2.7 million in reserve for future investments.

If each company's probability of success is p, the probability of exactly k successes out of n companies is (n choose k) pk (1-p)(n-k) where (n choose k) is n!/((n-k)! k!)

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