Chapter 11 Data Analysis and Statistics - 11.2 Apply Transformations to Data - 11.2 Exercises - Mixed Review - Page 755: 32

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The probability of tossing a coin 30 times and getting 21 heads can be found by applying: $P(X=21)=_nC_k p^k (1-p)^{n-k}\\=_{30} C_{21} 0.5^{21}(1-0.5)^{30-4}\\=\frac{30!}{(30-21)!.21!}\times0.5 ^{30}\\=0.013325$