Question

There are 169 million registered voters in the us. determine an interval for the number (how many) of registered democrats in the population. + answer

Answer 1

Part A:

Given that in a sample of 400 registered voters, 204 were democrats, i.e. n = 400, $\hat{p}= \frac{204}{400} =0.51$

The 95% confidence interval for the proportion of registered democrats voters in the population is given by:

$95\%\ C.I.=\hat{p}\pm z_{\alpha/2}\sqrt{\frac{\hat{p}(1-\hat{p})}{n}} \\ \\ =0.51\pm1.96\sqrt{\frac{0.51(1-0.51)}{400}}=0.51\pm1.96\sqrt{\frac{0.2499}{400}} \\ \\ =0.51\pm1.96(0.025)=0.51\pm0.049=(0.51-0.049,\ 0.51+0.049) \\ \\ =\bold{(0.461,\ 0.559)}$



Part B:

Given that there are 169 million registered voters in the US, the interval for the number of registered democrats in the population is given by

[0.461(169,000,000), 0.559(169,000,000)] = (77,909,000, 94,471,000)