Question 1152390
90% CI has z=1.645
SE is sqrt(p*(1-p)/n)
half-interval is 0.025
so 1.645*sqrt(0.85*0.15/n)=0.025
square everything
2.706*.1275/n=0.000625
so n=2.706*0.1275/0.000625=552.04 or 553 needed.