Need help on how to input invnorm and normalcdf using large numbers

In summary: Sorry I read the question incorrectly. It's asking you to find the top 90%, which is the same as the 10th percentile. When I read it I thought it was asking for the 90th percentile. So if you change your code to this it should work: invNorm (.10, 41182,19990)
  • #1
aprilryan
20
0
Hi,

I'm a little unsure how to input large numbers into the TI-83 calculator using invNorm and normalcdf. Here's the question to the problem:

A study of VCR owners found that their annual household incomes are normally distributed with a mean \$41,182 and a standard deviation of \$19,990.

a. What is the percentage of households with incomes between \$30,000 and \$50,000?

Of course this cannot be inputted as normalcdf (30000, 50000, 41182, 19990) can it?

b. If an advertising campaign is to be targeted at those VCR owners whose incomes are in the top 90%, find the minimum income level for this target group.

This one also cannot be invNorm (.90, 41182,19990) can it?

Thanks
 
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  • #2
Hi aprilryan,

a) I hadn't practiced this on the TI-83 before reading your question, but it seems this would be the correct syntax. What do you get for your answer? I can check it on another program.

b) Yes I believe this is the correct syntax. Again, I can check your answer if you wish.
 
  • #3
The answer for a is .3824. The answer for b is 66800.21 (which I can sense is wrong). Yes, could you please check the answers for me? Thanks again.
 
  • #4
aprilryan said:
The answer for a is .3824. The answer for b is 66800.21 (which I can sense is wrong). Yes, could you please check the answers for me? Thanks again.

I got the same answer for both! :) Looks good to me. Why do you think (b) is wrong? It's good to check the reasonability of an answer, so questioning your result is smart but in this case it is in fact correct.
 
  • #5
Well, I checked the answer key and for part b it says the answer is $15,564. Thanks again.
 
  • #6
aprilryan said:
Well, I checked the answer key and for part b it says the answer is $15,564. Thanks again.

Sorry I read the question incorrectly. It's asking you to find the top 90%, which is the same as the 10th percentile. When I read it I thought it was asking for the 90th percentile. So if you change your code to this it should work:

Code: 
 invNorm (.10, 41182,19990)
 
  • #7
I got it now! Thanks!
 

FAQ: Need help on how to input invnorm and normalcdf using large numbers

How do I use the invnorm function to input large numbers?

To input large numbers into the invnorm function, you will first need to determine the z-score for the desired probability. Then, use the formula z = (x - µ) / σ to solve for x. Once you have the value of x, you can input it into the invnorm function along with the mean (µ) and standard deviation (σ) of the normal distribution.

Can I use the normalcdf function to calculate probabilities for large numbers?

Yes, you can use the normalcdf function to calculate probabilities for large numbers. This function allows you to input the lower and upper bounds of the desired range, as well as the mean and standard deviation of the normal distribution, to calculate the probability of a random variable falling within that range.

What is the difference between invnorm and normalcdf when inputting large numbers?

The invnorm function is used to calculate the value of a specific data point (x) on a normal distribution, given the probability of that data point occurring. On the other hand, the normalcdf function is used to calculate the probability of a range of data points falling within a specified range.

How can I check if I input the correct values for invnorm and normalcdf when dealing with large numbers?

One way to check if you have input the correct values for invnorm and normalcdf when dealing with large numbers is to use a graphing calculator or statistical software to verify your results. You can also refer to a table of z-scores and probabilities to check your answers.

Are there any limitations when using invnorm and normalcdf for large numbers?

Yes, there are some limitations when using invnorm and normalcdf for large numbers. These functions assume that the data follows a normal distribution, so they may not be accurate for non-normal data. Additionally, if the numbers are extremely large, the calculations may become more complex and require specialized software or techniques.

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