John F. answered • 04/12/15

Business, standardized testing (SAT, GMAT) & statistics tutor

standard deviation of the sample = SQRT(p*q/n)

p = 73%

q = 1-p = 27%

n = 1800

SD = .010464 = 1.0464%

your differences (Xbar - mean) are + or - 3%

So your Z scores (+ and -) are:

Z+ = 3%/1.0464% = 2.87

Z- = -3%/1.0464% = -2.87

Use your Z table to look up the probabilities of these two Z scores

P+ = 0.9979

P- = 0.0021

difference (in between these 2 values) = .9959, or

**99.59%**