Holy crap for the last 48 hours, i have been doin nothing but doin all of your questions for yr 1 and yr 2 stats. Thank you for ur videos. Gotta keep up the grind, gonna move on to the T formula next (i hate fp1 man....)
We know that 15% are below 24.63, so this means that 15%+45%=60% are below k. We can also find sigma by doing the standardising process on the statement that 15% are below 24.63, and then use that value of sigma to do inverse normal to find k. It's a longer question than it first seems! Let me know if you need more guidance.
Because we are suspicious of that sample’s mean being larger than the stated mean, so we are interested in that value or larger. If it were 50.4 and smaller, the probability would be very high!
They aren’t symmetrical, so this can’t be done - there’s nothing in the question that says they are symmetrical, just that those ones can or cannot be used!
Because 50.4 is greater than the mean of 50.1, we are interested to know the probability of 50.4 or even more extreme/greater. The probability of the sample having a mean of 50.4 of lower is obviously going to be very high, as the mean is 50.1! We are looking for the small probability, not the large probability.
Sir for part a), instead of using inverse, i used the fact that 95% of the data lies within 2 standard deviations of the mean which gave me a mean of 49.98 instead, which i used in subsequent calculations. Do i still get marks for this, and if not then are those 3 facts we learn about in the beginning of the chapter basically redundant?
They are almost redundant, yes - you should always use the calculator, as this is how the questions are designed. It is useful to know those facts about the sd's of the normal distribution as it gives you a quick sense of the distribution, though!
Yes you can do critical regions for normal hypothesis tests - unless it asks for you to state the p-value, which is the probability that we found in this example to compare to the significance level.
Sir, also how do I identify binomial and normal distribution with X bar, is there a way. I thought in part b) of the question they were talking about normal distribution with X bar, instead it was the third question. Please can you clarify?
@@BicenMaths Sure, is there any clues I can use to determine whether they are asking me binomial instead of normal distribution with n => Xbar ~N(mu, sigma ²/n). because they both say a random sample of ... is chosen.
But we *observed* a mean of 50.4, so that's the thing we are investigating - try it with 50.1... as the mean we are assuming is correct is 50.1, we'll just get 50%, which isn't very helpful! :)
That’s it! Sometimes they don’t even tell you that you need to do this, you just have to spot that it’s absent from the distribution model you’re wanting to use, so you go find it!
Sorry but I can only really answer about questions in these videos, otherwise I might end up being asked things from all over the place, I hope that makes sense! :)
Holy crap for the last 48 hours, i have been doin nothing but doin all of your questions for yr 1 and yr 2 stats. Thank you for ur videos.
Gotta keep up the grind, gonna move on to the T formula next (i hate fp1 man....)
You are so welcome! I love to hear these updates from people using my videos, keep it up! 👏🏼
Also I am not a fan of t-formulae and have been putting off teaching it on here 😅
@@BicenMaths honestly t formula and the entirerity of fm1 is easy to get but very janky and prone to technical errors 😓. But alas i need to work on em
Same, so easy to make errors with t formulae!
@Safe Sword good to see you here😅
At 8:22 for question 5a, how would you obtain the a value of -1.0364 as I got -2.17
We know that 15% are below 24.63, so this means that 15%+45%=60% are below k. We can also find sigma by doing the standardising process on the statement that 15% are below 24.63, and then use that value of sigma to do inverse normal to find k. It's a longer question than it first seems! Let me know if you need more guidance.
Sir at 5:43, why do you test for the probability of y-bar being greater than 50.4?
Because we are suspicious of that sample’s mean being larger than the stated mean, so we are interested in that value or larger. If it were 50.4 and smaller, the probability would be very high!
@@BicenMaths of course. My bad sir, and thanks for the reply.
No problem!
Sir at 3:52 why is it less than 3 and not less than 3.5 as we are doing binomial from normal?
We only do continuity correction if we are going from discrete to continuous - this is going from continuous to discrete!
Sir, to find the mean can't you do (49+50.75)/2 =49.875, because they are symmetrical?
They aren’t symmetrical, so this can’t be done - there’s nothing in the question that says they are symmetrical, just that those ones can or cannot be used!
5:38, how did you know to put Y bar as greater than 50.4, and not less than?
Because 50.4 is greater than the mean of 50.1, we are interested to know the probability of 50.4 or even more extreme/greater. The probability of the sample having a mean of 50.4 of lower is obviously going to be very high, as the mean is 50.1! We are looking for the small probability, not the large probability.
Sir for part a), instead of using inverse, i used the fact that 95% of the data lies within 2 standard deviations of the mean which gave me a mean of 49.98 instead, which i used in subsequent calculations. Do i still get marks for this, and if not then are those 3 facts we learn about in the beginning of the chapter basically redundant?
They are almost redundant, yes - you should always use the calculator, as this is how the questions are designed. It is useful to know those facts about the sd's of the normal distribution as it gives you a quick sense of the distribution, though!
@@BicenMaths Ohhh I see! Thanks for the help 🙏
could you do part c by calculating the critical region instead or does that just happen to give the right answer in this case?
Yes you can do critical regions for normal hypothesis tests - unless it asks for you to state the p-value, which is the probability that we found in this example to compare to the significance level.
Also Sir do you have a video going through the conditional probabilities bit at the back of the booklet as I can't find one?
I don’t, I’m afraid! Sorry!
Sir, I get confused what values you use for mu and X bar, why do we use those values?
mu is the mean average of the whole population, whereas x bar is the mean average of the sample taken from the whole population
Hi Sir I am bit confused when you did part (a) you just used the range 49
Because part a is continuous, so it doesn’t matter if you use < or
Sir, also how do I identify binomial and normal distribution with X bar, is there a way. I thought in part b) of the question they were talking about normal distribution with X bar, instead it was the third question. Please can you clarify?
I’m sorry, I’m not sure I understand your question - can you rephrase?
@@BicenMaths Sure, is there any clues I can use to determine whether they are asking me binomial instead of normal distribution with n => Xbar ~N(mu, sigma ²/n).
because they both say a random sample of ... is chosen.
Ohhh I see - you’d only use the normal one you’ve just said if you are doing the hypothesis test on the mean.
Love your videos!! I have a question, for part c, why is your P(Y>50.4) , I thought we were testing if it is greater than 50.1
But we *observed* a mean of 50.4, so that's the thing we are investigating - try it with 50.1... as the mean we are assuming is correct is 50.1, we'll just get 50%, which isn't very helpful! :)
So whenever we have unknown sigma or mu , we think of z values and standard normal distribution
That’s it! Sometimes they don’t even tell you that you need to do this, you just have to spot that it’s absent from the distribution model you’re wanting to use, so you go find it!
@@BicenMaths yes I noticed they are sneaky about it , I will keep it in mind
Sir, I was doing this question from S1 Edexcel January 213 Q5 part (f) I don't know how to go about it could you please explain it to me ?
Sorry but I can only really answer about questions in these videos, otherwise I might end up being asked things from all over the place, I hope that makes sense! :)
@@BicenMaths I just saw this comment Sir, I understand, thank you for the videos sir.