Wrong subject, but that is true. You should have information to back that up also.
x = number of hours
want to find probability (P) x >= 13
x is N(14,1) transform to N(0,1) using z = (x - mean) / standard deviation so can look up probability using standard normal probability table.
P(x >= 13) = P( z > (13 - 14)/1) = P(z > -1) = 1 - P(z < -1) = 1 - 0.1587 = 0.8413
To convert that to percentage, multiply 100, to get 84.13%
If you would like to solve the system of equations, you can do this using the following steps:
4x^2 + 9y^2 = 72
2x - y = 4 ... 2x - 4 = y
_________
<span>4x^2 + 9y^2 = 72
</span><span>4x^2 + 9 * (2x - 4)^2 = 72
</span>4x^2 + 9 * (4x^2 - 16x + 16) = 72
4x^2 + 36x^2 - 144x + 144 = 72
40x^2 - 144x + 144 - 72 = 0
40x^2 - 144x + 72 = 0
10x^2 - 36x + 18 = 0
5x^2 - 18x + 9 = 0
(5x - 3) * (x - 3) = 0
1. 5x - 3 = 0 ... 5x = 3 ... x = 3/5
2. x = 3
<span>1. y = 2x - 4 = 2 * 3/5 - 4 = 6/5 - 20/5 = -14/5
2. y = 2x - 4 = 2 * 3 - 4 = 6 - 4 = 2
1. (x, y) = (3/5, -14/5)
2. (x, y) = (3, 2)
The correct result would be </span>(3/5, -14/5) and <span>(3, 2).</span>
Answer:
First, determine how many standard deviations above the mean one would have to be to be in the 75th percentile. This can be found by using a z table and finding the z associated with 0.75. The value of z is 0.674. Thus, one must be .674 standard deviations above the mean to be in the 75th percentile
