document.write( "Question 1094896: A report in 2010 indicates that Americans between the ages of 8 and 18 spend an average of μ = 10 hours per day using some sort of electronic devices such as smart phones, computers, or tablets. Assume that the distribution of times is normal with a standard deviation of σ = 2.5 hours and find the following values.\r
\n" ); document.write( "\n" ); document.write( "A. What is the probability of selecting an individual who uses electronic devices more than 12 hours a day?
\n" ); document.write( "So far for this one, I have done (9-10)/ 2.5= 1.8. I am not sure what to do from here. I am pretty sure I have to subtract a z score amount from the z table, but I'm not really sure how to figure that out.
\n" ); document.write( "B. What proportion of 8- to 18-year-old Americans spend between 8 and 12 hours per day using electronic devices? P(5\n" ); document.write( "I am really confused by this question, I'm not sure where to start. \n" ); document.write( "

Algebra.Com's Answer #834600 by ikleyn(52777) $\"\"$ $\"About$

You can put this solution on YOUR website!
.
\n" ); document.write( "A report in 2010 indicates that Americans between the ages of 8 and 18
\n" ); document.write( "spend an average of μ = 10 hours per day using some sort of electronic devices
\n" ); document.write( "such as smart phones, computers, or tablets.
\n" ); document.write( "Assume that the distribution of times is normal with a standard deviation
\n" ); document.write( "of σ = 2.5 hours and find the following values.
\n" ); document.write( "A. What is the probability of selecting an individual who uses electronic devices
\n" ); document.write( "more than 12 hours a day?
\n" ); document.write( "So far for this one, I have done (9-10)/ 2.5= 1.8. I am not sure
\n" ); document.write( "what to do from here. I am pretty sure I have to subtract a z score amount
\n" ); document.write( "from the z table, but I'm not really sure how to figure that out.
\n" ); document.write( "B. What proportion of 8- to 18-year-old Americans spend between 8 and 12 hours per day
\n" ); document.write( "using electronic devices?
\n" ); document.write( "P(5 I am really confused by this question, I'm not sure where to start.
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\n" ); document.write( "\n" ); document.write( "Each normal probability curve is bell shaped curve.\r
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\n" ); document.write( "\n" ); document.write( "For task (A), you goal is to find the area under this curve on the right
\n" ); document.write( "of z-mark 12 hours.\r
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\n" ); document.write( "\n" ); document.write( "For task (B), you goal is to find the area under this curve between
\n" ); document.write( "z-marks 8 and 12 hours.\r
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\n" ); document.write( "\n" ); document.write( "Each of these areas is the solution/(the answer) to the relevant question.\r
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\n" ); document.write( "\n" ); document.write( "There are different ways to solve this and similar problems.\r
\n" ); document.write( "\n" ); document.write( "I will show/describe some of them in this my post.\r
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\n" ); document.write( "\n" ); document.write( "                    These ways are \r
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\n" ); document.write( "\n" ); document.write( "        (1) using table for cumulative normal distribution function;
\n" ); document.write( "        (2) using calculators like     TI-83     and/or     TI-84.
\n" ); document.write( "        (3) using online calculators from the Internet web-sites.\r
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\n" ); document.write( "\n" ); document.write( "The best way to start is to use an online calculator from this web-site\r
\n" ); document.write( "\n" ); document.write( "https://onlinestatbook.com/2/calculators/normal_dist.html\r
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document.write( "So, go to that web-site.\r\n" );
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document.write( "There is an online free of charge calculator there with simple and intuitively clear interface.\r\n" );
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document.write( "In the calculator, input the mean value 10 hours and standard deviation value of 2.5 hours \r\n" );
document.write( "in the corresponding port windows.\r\n" );
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document.write( "For question (A), input 12 in the port \"Above\".\r\n" );
document.write( "Then click \"Recalculate\".\r\n" );
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document.write( "You will get the answer 0.2119 for the probability and the corresponding diagram, showing \r\n" );
document.write( "the area of interest.\r\n" );
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document.write( "\r\n" );
document.write( "      +----------------------------------------------+\r\n" );
document.write( "      |    In this way, the problem is just solved,  |\r\n" );
document.write( "      |    and you just learned your first lesson.   |\r\n" );
document.write( "      +----------------------------------------------+\r\n" );
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document.write( "Next, if you want to use the table for cumulative normal distribution function,\r\n" );
document.write( "\r\n" );
document.write( "you should calculate z-score  z =  =  = 0.8.\r\n" );
document.write( "\r\n" );
document.write( "From the table, you will find the corresponding value of the cumulative normal distribution function 0.7881.\r\n" );
document.write( "\r\n" );
document.write( "    Remember that it is the area to the LEFT of the mark 0.8, \r\n" );
document.write( "    while you need the area on the RIGH of this mark.\r\n" );
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document.write( "So, you subtract the value 0.7881 from 1, and you get your answer 1 - 0.7881 = 0.2119,\r\n" );
document.write( "which is THE SAME, as the online calculator gave you above (!)\r\n" );
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document.write( "And finally, the last way solving with the calculators as TI-83 and/or TI-84.\r\n" );
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document.write( "A function to use in such calculators is normalcdf(z1, z2, mean, SD)  \r\n" );
document.write( "    // \"cdf\" stands for cumulative distribution function.\r\n" );
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document.write( "In the calculator, your input is normalcdf(12, 9999, 10, 2.5).\r\n" );
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document.write( "The calculator will give you the answer (the probability) 0.2119.\r\n" );
document.write( "

\r
\n" ); document.write( "\n" ); document.write( "So, I answered and explained EVERYTHING to you, which relates to your question (A).\r
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\n" ); document.write( "\n" ); document.write( "For instructions on using this function normalcdf, if you need them, see the link
\n" ); document.write( "https://www.usu.edu/math/cfairbourn/calculatorhelps/normalcdfti-84.pdf\r
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\n" ); document.write( "\n" ); document.write( "In the future, post your separate questions SEPARATELY in separate posts.\r
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\n" ); document.write( "\n" ); document.write( "It will guarantee you that you will get exhaustive, exact, clear answers (and not a MESS).\r
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