Question 1201712
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TWIN problems were solved many times at this forum.  

Below is a short list of solutions (probably, not full list)


https://www.algebra.com/algebra/homework/Probability-and-statistics/Probability-and-statistics.faq.question.1189932.html


https://www.algebra.com/algebra/homework/Probability-and-statistics/Probability-and-statistics.faq.question.1079027.html


https://www.algebra.com/algebra/homework/Probability-and-statistics/Probability-and-statistics.faq.question.1175460.html


https://www.algebra.com/algebra/homework/Probability-and-statistics/Probability-and-statistics.faq.question.1109598.html



Happy learning (!)