Posted by **Andrea** on Wednesday, January 28, 2009 at 8:08pm.

I saw that this was already answered but I can't find it if anyone knows, can you point me in the right direction?

A recent poll of 700 people who work indoors found that 278 of them smoke.If the researchers want to be 98% confident of thier results to within 3.5%, how large a sample is necessary?

- College Statistics 2 -
**MathGuru**, Wednesday, January 28, 2009 at 10:17pm
Here's one formula you can use for a problem of this type:

n = [(z-value)^2 * p * q]/E^2

Note: n = sample size needed; ^2 = squared; .4 for p and .6 for q (q = 1 - p). E = maximum error, which is .035 (3.5%) in the problem. Z-value is found using a z-table (find the value that corresponds to 98% confidence). Substitute into the formula. Round your answer to the next highest whole number.

Note: 278/700 is approximately .4 in decimal form.

I hope this will help.

- Elementary Statistics -
**Roxanne Singleton**, Monday, November 2, 2009 at 9:46am
2. A research team studied the ages of patients who had heart attacks caused by smoking. The ages of 34 patients who suffered a heart attack were as follows.

29 30 36 41 45 50 57 61 28 50 66 58

60 38 36 47 40 32 58 46 61 40 55 32

61 56 45 46 62 66 38 40 40 27

Construct a Stem-and-Leaf Plot using this data with Key: 5 | 7 = 57.

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