Answer:
So H have to equale to 0
and ![t> 0](https://tex.z-dn.net/?f=t%3E%200)
![-4,9t^2+33,6t+4,9=0\\\Delta=33,6^2+4*4,9*4,9=1225\\\sqrt{\Delta }=35\\t=\frac{-33,6-35}{2*(-4,9)} =14s](https://tex.z-dn.net/?f=-4%2C9t%5E2%2B33%2C6t%2B4%2C9%3D0%5C%5C%5CDelta%3D33%2C6%5E2%2B4%2A4%2C9%2A4%2C9%3D1225%5C%5C%5Csqrt%7B%5CDelta%20%7D%3D35%5C%5Ct%3D%5Cfrac%7B-33%2C6-35%7D%7B2%2A%28-4%2C9%29%7D%20%20%3D14s)
Step-by-step explanation:
Answer:
I think b
Step-by-step explanation:
<h3>
Answer: 1/4</h3>
=================================================
Explanation:
Let's say this school has 1000 students.
5/8 of that amount is (5/8)*1000 = 625. There are 625 students who play sports.
Then we take 2/5 of this to get (2/5)*625 = 250 to represent the number of people who play soccer.
The last step is to divide that result over the original number of students. Reduce as much as possible.
250/1000 = 25/100 = 1/4
Therefore, 1/4 of all the students play soccer
I'm guessing you intended to say
has mean
and standard deviation
, and
has means
and standard deviation
.
If
, then
has mean
![E[W]=E[X+Y]=E[X]+E[Y]=55](https://tex.z-dn.net/?f=E%5BW%5D%3DE%5BX%2BY%5D%3DE%5BX%5D%2BE%5BY%5D%3D55)
and variance
![\mathrm{Var}[W]=E[(W-E[W])^2]=E[W^2]-E[W]^2](https://tex.z-dn.net/?f=%5Cmathrm%7BVar%7D%5BW%5D%3DE%5B%28W-E%5BW%5D%29%5E2%5D%3DE%5BW%5E2%5D-E%5BW%5D%5E2)
Given that
and
, we have
![\mathrm{Var}[X]=E[X^2]-E[X]^2\implies E[X^2]=36+25^2=661](https://tex.z-dn.net/?f=%5Cmathrm%7BVar%7D%5BX%5D%3DE%5BX%5E2%5D-E%5BX%5D%5E2%5Cimplies%20E%5BX%5E2%5D%3D36%2B25%5E2%3D661)
![\mathrm{Var}[Y]=E[Y^2]-E[Y]^2\implies E[Y^2]=16+30^2=916](https://tex.z-dn.net/?f=%5Cmathrm%7BVar%7D%5BY%5D%3DE%5BY%5E2%5D-E%5BY%5D%5E2%5Cimplies%20E%5BY%5E2%5D%3D16%2B30%5E2%3D916)
Then
![E[W^2]=E[(X+Y)^2]=E[X^2]+2E[XY]+E[Y^2]](https://tex.z-dn.net/?f=E%5BW%5E2%5D%3DE%5B%28X%2BY%29%5E2%5D%3DE%5BX%5E2%5D%2B2E%5BXY%5D%2BE%5BY%5E2%5D)
and
are independent, so
, and
![E[W^2]=E[X^2]+2E[X]E[Y]+E[Y^2]=661+2\cdot25\cdot30+916=3077](https://tex.z-dn.net/?f=E%5BW%5E2%5D%3DE%5BX%5E2%5D%2B2E%5BX%5DE%5BY%5D%2BE%5BY%5E2%5D%3D661%2B2%5Ccdot25%5Ccdot30%2B916%3D3077)
so that the variance, and hence standard deviation, are
![\mathrm{Var}[W]=3077-55^2=52](https://tex.z-dn.net/?f=%5Cmathrm%7BVar%7D%5BW%5D%3D3077-55%5E2%3D52)
![\implies\sqrt{\mathrm{Var}[W]}=\sqrt{52}=\boxed{2\sqrt{13}}](https://tex.z-dn.net/?f=%5Cimplies%5Csqrt%7B%5Cmathrm%7BVar%7D%5BW%5D%7D%3D%5Csqrt%7B52%7D%3D%5Cboxed%7B2%5Csqrt%7B13%7D%7D)
# # #
Alternatively, if you've already learned about the variance of linear combinations of random variables, that is
![\mathrm{Var}[aX+bY]=a^2\mathrm{Var}[X]+b^2\mathrm{Var}[Y]](https://tex.z-dn.net/?f=%5Cmathrm%7BVar%7D%5BaX%2BbY%5D%3Da%5E2%5Cmathrm%7BVar%7D%5BX%5D%2Bb%5E2%5Cmathrm%7BVar%7D%5BY%5D)
then the variance of
is simply the sum of the variances of
and
,
, and so the standard deviation is again
.
Because the earth is round, the distance seen on a flat map is a lot further than the distance on a globe, because of distortion. So following the circle that goes through these 3 points ( Florida, Alaska and the Philippines) it is a shorter distance to fly over Alaska.