Everyone. So today we're gonna be doing a similar question to the previous video. But we're searching for the population standard deviation rather than looking for the sample me. And so I'm just gonna write out the information we're given in the question. So we're given. I bought. Sees fictional M U is equal to 16. H a mu is less than 16 were given that it's a sample of 50. So and it's 50 we're told that Expo is 14 Onda. We are given a P value off. No point, not 17 Now the first thing we need to do is convert this P value into a said start value. I would do this using the inverse normal, which I talked a little bit about when I answered question 19 So I'd look back to that if you want a little bit of an idea what's going on with this calculation? But you basically put it into calculator and you get it out is 2.120 what, So now we gotta set style value, and we also have a handy said star formula so we can use this formula here, and the values that we've got available to us to isolate the value of Sigma. So if I write this set style value here on the left hand side, right, 2.1 to 1 is equal to And then we know what experience. Because we were told it was 14 over here. And we know what Mu is because you were told what Mu is, that's 16. Now we're looking for Sigma and we've been told that and it's 50. And so we've got Sigma. Now, this is a little bit harder than just isolating the sample mean because this is in the center, off a off double decker fraction. Essentially. And so what we want to do is to start off with. I'm just gonna I'm gonna move this fraction here to the left hand side. This might seem counterintuitive, cause surely we want to get this on this side, but it's more helpful to get rid of this fraction this larger fraction in the first place than it is to do anything else first. So what you're then have is 2.1 to 1. We'll have, uh, sigma over 50 here and then 14 minus 60 is minus two. We can do that in our heads. And so then we can up. We can move this to the other side here by dividing, if you can believe me, that's a division symbol. Should try that somewhere else by dividing. That's it then what we have is Sigma over 15 built right? All of this is right now, my dio sigma over great 50 is equal to, uh to over 2.1201 And so then we can get rid of the bottom of this direction by just multiplying over here, just as we would normally, if this was a normal fraction, it might help you toe sort of visualize what I mean. I haven't put these brackets on here. So what we have is just too normal fractions. I could multiply both by route 50 to isolate sick my hair. So then we have Sigma is to route 50 over 2.1201 on. Then you just put the anti calculator and you get out is 6.6706 And that is our standard deviation in this question and again a little bit harder than the previous one. Looking at the sample mean? But we've been given all the information we need. Remembering how to convert for a P value to Azad style value on then just rearranging this equation until you can plug it into your calculator on. There you have it.