Answer:
Mean is 81%
standard deviation is approximately 4.2%
Step-by-step explanation:
Since the number of boys equals the number of girls, but it is not given, we name it "N". and proceed to calculate the mean as:
Mean = (0.78 * N + 0.84 * N) /(2 N)
using that the total number of students must be N boys + N girls = 2 N
Then the Mean becomes: N *(0.78 + 0.84) /(2 N) = (0.78 + 0.84) / 2 = 1.62 / 2 = 0.81
So the mean is 81%
Now, standard deviation will be calculated by first adding the squares of the deviations: (X-0.81)^2 for the N boys and for the N girls, and then finding the square root of this and finally dividing by the square root of N. That is:

Now finding the square root of this value, and finally dividing it by the square root of N:

which in percent form is: approximately 4.2%
Answer:
Six hundred eighty-four thousand two hundred ninety-seventh
I do not understand why you or your teacher have written down a certain number of minutes by each equation, but I will do my best to answer your question. I hope that I’m able to help.
1,2) 20 + 3.5x = 30 + 2.75x
-20 -20
3.5x = 30 + 2.75x - 20
-2.75x -2.75x
0.75x = 10
/0.75 /0.75
x = 13.333...
3,4) 3.5x + 2.75x = 20 + 30
6.25x = 50
/6.25. /6.25
x = 8
Answer:
answer for 8 is 1500
Step-by-step explanation:
You just divide 4 by 8, which equals 1/2