Very helpful. I love how you demostrate on the bell curve so that I can "picutre" what you are saying. I will probably pass my statistics class because of your videos. Thank you for breaking it down and making it understandable!!!
Tnx Sir. In the first problem, letter "a", if I want to know exactly how many bulbs have 1800 lumens?( Z score = 2.58). How do I calculate that? I don't look for areas. Tnx again.
At 05:57 Is this in chronological steps in order STEP III P(x>1800) STEP IV=p(z score?>2.58) the 2nd equation LINE 2/3 to the last graphed step leading up to next? 1-.9951 as STEP V?
Hi my name is Joshua. I am thinking about taking stats 245 at Northern VA community College. Any suggests on what kinds of problems regarding a scores, probabilities, standard deviations etc..? I would like some help on this subject? Thanks for your help
Brilliant, thanks for this. I'm doing revision so I was able to work out the sum at the start when you had the values it up on screen before you went through it and then see if I was right.
Assume that 21-year-old men's heart rates at rest are normally distributed with a mean of 63 beats per minute and a standard deviation of 10 beats per minute. If 600 men are examined, how many would you expect to have a heart rate of less than 68?
I tried so many different thinggs to understand this process whike studing for my exam. I was ready to give up until I watched this video. A light switch finally flipped on. 😅 understand this process until I saw this
this is helpful but i am a little stuck trying to draw 2 distributions to compare, the range is 19-24 mean 21.5 standard deviation of 2, then the 2nd drawing needs to show the same range but a mean of 21.8 and standard deviation of 1, i have to compare the 2 and see which set of figures gives better results with average falling towards 22, any help would be incredible
You are probably using a different z-table than I am using. The one you are using is giving you the area under the curve from the z-score to the mean. The z-table I am using is giving me the area under the curve to the left of the z-score. If you add .5 to your z-score, you will get the same answer as I do. Hope this helps.
and what if there's no definite value unlike 1800, i mean if it just says for example what is the probability that 50 of 100 watt lightbulbs will have a brightness more than the average brightness of 1640 lumens?
Good luck in your class. Go to my RU-vid channel and click on about and then go to my website and then click on statistics video and I have them organized.
when i tried for solving the probability of two values i tried to follow what you have done in problem c but the result of my computation is negative. is it allowed to have a negative value for area after subtracting the 2 values, the one w/ between? thank you so much
Why did you subtract the result of problem a to 1 (more than) while in b you don’t do the subtraction thing? Thank you so much. The given problem to us really confuses me a lot
May be a stupid question, but I need to understand this for my MBA that I'm starting. Why in the first problem is it subtracted from 1, but in the second part it's simply the Z table without subtracting from 1? I think I know the answer, but would like to confirm. Thanks!
@@crowsmathclass Sorry to bother once more, but how do you determine when to subtract from one based upon the question? For instance, I missed a lot of my questions because I didn't subtract with 1, but got some right by not doing so. How do I know when to subtract 1 from n? Is this understanding when a problem is dealing with the population as opposed to a sample? Sorry, my MBA is online, I have two degrees and swore I'd never do anything dealing with numbers again..., so here I am, lol. Thank you so much for any info you can provide!
Great video. But I got a question. We're comparing how far or close the sample mean is relative to the population mean. The distance to either side of the population mean is 0.5000. If we're comparing the sample mean with the population mean, which has a z-value score of 0, why we're taking the whole area under the curve while calculating less than or greater than areas under the curve from the population mean? Shouldn't we be calculating areas under the curve relative to the population mean (z-value = 0), not the whole area under the curve?
