As of 2023, the population of Singapore is approximately 5.64 million and the population of Malaysia is approximately 33.57 million.

1. Find the total population in millions.

$5.64+33.57=39.21$
So the total population is $39.21$ million.

2. Convert the total population to standard form.

$39.21\text{ million}=39.21\times 10^{6}=3.921\times 10^{7}$

1. Represent the 2023 population as a percentage of the 2013 population.

Since the 2023 population was $5\%$ more than the 2013 population,

$\text{2023 population} = 105\% \text{ of 2013 population}$.

So $5.64$ million represents $105\%$ of the 2013 population.

2. Divide by 105% to find the 2013 population.

$\text{2013 population} = 5.64 \div 1.05$

$= 5.371428571\ldots \text{ million}$