00:01
So this question we're told that x has a probability density function, f of x is 1 over root 2 pi sigma e to the minus x minus mu squared over 2 sigma squared.
00:14
Now that means that x is normal with a mean of mu and a variance of sigma squared.
00:21
Now let's write down that y is ax plus b, then the distribution function of y, which is the probability that y is less than or equal to y, is going to be the probability that x obeys ax plus b is less than or equal to y.
00:42
So that's the probability that ax is less than or equal to y minus b, which is the probability that x is less than or equal to y minus b over a.
00:55
So that is going to be the integral from minus infinity to y minus b over a of 1 over root 2 pi sigma e to the minus x minus mu squared over 2 sigma squared dx.
01:11
So now we can apply the fundamental theorem of calculus.
01:19
So f y of y is d f y of y by dy.
01:25
So what we're going to do is evaluate at the upper limit 1 over root 2 pi sigma e to the minus y minus b over a minus mu squared over 2 sigma squared times the derivative of this, which is 1 over a.
01:45
So let's recombine all this.
01:52
1 over 2 pi a sigma e to the minus, then we've got y minus b minus a mu.
02:01
So that's y minus b plus a mu squared.
02:06
And i've pulled out the a squared, so it's over 2 a sigma squared.
02:12
And that tells us that y is normal with a mean of b plus a mu and a variance of a sigma squared.
02:23
A squared sigma squared.
02:25
It's going to be the variance...