Question 1075549
the interval is +/- z*sqrt{p*(1-p)/n}
That is 1.96*sqrt(0.52*0.48)/n=0.04, the size of the interval.
square everything and then multiply both sides by n
3.8416(.2496)=0.0016n
divide both sides by 0.0016
599.29 rounded to 600.
Calculator for the calculations.
Can check with calculator for 1 sample proportion using 312 and 600 (52%) then asking for 95% CI.  The interval is 4% on either side. of 52%.