Question

The number of sit-ups that all tenth-grade girls can do in 5 minutes is normally distributed. Beth surveyed 20 of her fellow intramural tennis players, all tenth-grade girls, and determined the mean number of sit-ups they could do. Can she make an inference about the population mean for all tenth-grade girls based on the sample?
No, because the sample size was not big enough.
No, because she did not use a simple random sample.
Yes, because the sample size was big enough.
Yes, because she used a simple random sample.

Answer 1

Please help, i will give medal and fan.

Answer 2

@kropot72 help whenever you are available

Answer 3

I think it's No didn't use a random sample.

Answer 4

However, when I took stats my instructor said sample size had to be at least 30+ but of course I think this was just a rule of thumb. Lol

Answer 5

@kropot72 do you have any words of wisdom for OP?

Answer 6

I was going to say it was random, but yeah, it's not - all 10th graders vs 10th grade tennis players (who could prob do more situps on average).

Answer 7

When I did stat, I was also told about the 30+ rule.

Answer 8

If the population is known to be normally distributed, as it is in this question, then sample quantities a little less than 30 can be used to make inferences. The requirement for sample sizes at least 30 comes into play when the Central Limit Theorem must be used.

Answer 9

I thought the sample was biased and we don't want that.

Answer 10

@kropot72 ahhh you have a great point.

Answer 11

I agree what @kropot72 said :#

Answer 12

So D?

Answer 13

I would incline to choice C in this case.

Answer 14

thank you kropot , always coming to the rescue

Answer 15

You're welcome :)