if the mean is 70 minutes, then 90 minutes is 2 standard deviations above 70. if you look at the bell curve i drew, the percent of exams that took over 90 minutes is 2.5%
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1) an = a1 + d*(n-1) => a20 = -4 + (-9)*19 = -4 - 171 = - 175
1) ---> C)
2) a81 = 20 + 4*80 = 340;
2) ---> A)
3) a12 = ?
3) ---> B) or D).
Thank you for posting your question here at brainly. I hope the answer will help you. Feel free to ask more questions here.
Below is the solution:
xdy/dx = 4y
<span>xdy = 4ydx </span>
<span>∫ dy/y =∫ 4dx/x </span>
<span>ln(y) = 4ln(x) + C </span>
<span>y = e^[4ln(x)] e^C </span>
<span>y = e^[ln(x)^4] e^C </span>
<span>y = Cx^4 answer</span>
For the first digit, you have two possible choices: 1 or 2. For *each* of those choices, you can choose 1 or 2 for the second digit in the number, and for each of *those*, you can choose 1 or 2 for the third digit of the number.
That’s 2 * 2 * 2 or 8 possible 3-digit numbers you can make with the digits 1 and 2.
12-13 I hope this helps ;)
