The two were born, one just before and the other just after midnight, on a ship that sailed over the international date line sometime between their births.

The passage of midnight and the crossing of the date line each contributed 1 day difference in their birth dates.

Yes. 9, 11 and 13. Numbers that average slightly more than 10, where 10*10*10 = 1000..

He packs the rod in a box that is 5 feet in length and 11 inches wide.
Such a box has a 61-inch diagonal.

After 300 miles, at 30 miles/gal, 10 gallons were consumed by the engine.
The other 15 gallons leaked,
And since he drove for 5 hours (300 mi at 60 mph), the gas leaked at the rate of 3 gal/hour.

The clock that is calculably slow is as good as a perfect one. You only need to know the date that it was set to the correct time. From that you can deduce the current correct time.

The clock that is broken has no value. True, it is correct twice a day, but we have no idea what those times are. Useless.

The answer is given in the question:
Assuming probability of having a boy or a girl is the same, then after a long time, there will be equal numbers of boys and girls.

Why should anyone think that decisions about when to start or stop having children has any effect on their gender?