clc
p=206/840
disp('q=1-p')
q=1-p
n=840
disp('standard error of the population of families having a monthly income of rs. 250 or less=(p*q/n)^0.5=')
(p*q/n)^0.5
disp('hence taking 103/420 to be the estimate of families having a monthly income of rs. 250 or less,the limits are 20% and 29%  approximately')