Question

Hi. Please help with these 4 problems. I keep getting the incorrect answer and i dont know what I am doing wrong :( Thank you in advance.

1) You want to obtain a sample to estimate a population proportion. Based on previous evidence you believe the population proportion is approximately p= 0.31. You would like to be 90% confident that your estimate is within 2.5% of the true population proportion. How large of a sample size required.

I got 932 but its incorrect!

2) you want to obtain a sample to estimate a population proportion. Based on previous evidence you believe the population proportion is approximately 15%. You would like to be 90% confident that your estimate is within 1% of true population proportion. How much of a sample size is required.

I got n= 3472 but its wrong.

3) You want to obtain a sample to estimate a population mean. Based on previous evidence you believe the population standard deviation is approximately 52.5. You would like to be 98% confident that your estimate is within 1.5 of true population mean. How large of a sample size required?

Lastly,

4) you want to obtain a sample to estimate how many parents spend on their kids birthday parties. Based on previous study you believe the population standard deviation is approximately $53.4. You would like to be 98% confident that your estimate is within 4 dollars of average spending on the birthday parties. How many parents do you have to sample?

Answer 1