From 1929 to 1933 the number of schools nearly doubled.

In the next 12 years, that number would double to 239.

By the turn of the 20th century the number had doubled.

The number of international phone calls has been growing at 20 percent a year and doubled every four years in the 1980's.

By the following summer the number had doubled to 10,000.

The number has at least doubled since then, with many more 20- and 30-somethings going to watch.

Since 1990 the number of students has more than doubled.

At the current rate, human numbers will double in about 40 years.

Today there are more than a million, and that number could double in three years.

But the number of men had doubled from the year before, to 1,917.