Question 1086022
95%CI is mean +/-1.96*SE
mean is point estimate, here 0.70
SE is sqrt (p*(1-p))/n, or sqrt (.21/250)=0.0290
interval width is 0.0568, after multiplying by 1.96
CI is {0.643, 0.757)
No, 50% is not a possible proportion.  It is not in the interval.