significance level of a= 0.05 to test the claim that p1 = p2 . In a vote on the Clean Water bill, 49% of the 205 Democrats voted for the bill while 41% of the 230 Republicans voted for it

Answer 1

this is a two-proportion z-test.

phat1 = 0.49

phat2 = 0.41

phat = (0.49 * 205 + 0.41 * 230) / (205 + 230)

test statistic z = (phat1 - phat2)/sqrt(phat*(1-phat)(1/205 + 1/230))

two sided test so reject Ho if |z| > 1.96 or if p-value < 0.05.