Posted by **Ashley** on Thursday, June 30, 2011 at 2:13pm.

The proportion of baby boys born in the United States has historically been 0.512. You choose an SRS of 55 newborn babies and find that 47% are boys. Do ALL calculations to 5 decimal places before rounding.

(d) In a random sample of 55 newborn babies, what is the probability that 47% of the sample are boys. (Use 3 decimal places). Hint: you are asked to find P( < .47 ). To calculate this first find the z-score and then look up the answer in the Z table.

- statistics -
**MathGuru**, Thursday, June 30, 2011 at 5:40pm
Formula for z-score:

z = (x - mean)/sd

Find mean:

mean = np = (55)(0.512) = ?

Find standard deviation:

sd = √npq = √(55)(0.512)(0.488) = ?

Note: q = 1 - p

Finish both calculations.

Substitute mean and standard deviation into the z-formula. Use 25.85 for x (0.47 * 55 = 25.85).

Once you have the z-score, use the z-table to determine your probability.

I hope this will help get you started.

- statistics -
**Ashley**, Thursday, June 30, 2011 at 8:32pm
Thank you sooo much!! Also thanks for posting steps and not just an answer.

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