Solution

Statement I : LAT MALES in city A = $27x$ and females in city A = $23x$

=> $27x - 23x = 1,00,000$

=> $x = \frac{1,00,000}{4} = 25,000$

$\therefore$ Total population of city A = $27x + 23x = 50x$

= $50 \times 25,000 = 12,50,000$

=> Statement I ALONE is sufficient.

Statement II : Let population of city B = $100x$

=> Population of city A = $\frac{80}{100} \times 100x = 80x$

=> $100x - 80x = 3,12,500$

=> $x = \frac{3,12,500}{20} = 15,625$

$\therefore$ Population of city A = $80 \times 15,625 = 12,50,000$

=> Statement II alone is sufficient.

$\therefore$ Either statement alone is sufficient.