Keifitz problem is solved

она, правда, была примером применения логарифма, но, тем не менее, осталась и часто обсуждалась на просторах сетевых ресурсов

This article is an updated version of one of the most popular features on PRB’s website, estimating the number of people who have ever been born. We first made this estimate in 1995, with updates in 2002 and 2011.

решила Toshiko Kaneda из PRB (на фотке)

Решение:

Given the current global population of about 7.5 billion (based on our most recent estimate as of mid-2017), that means those of us currently alive represent about 7 percent of the total number of humans who have ever lived.

PRB estimates that by 2050 about 113 billion people will have ever lived on Earth. 

How Many People Have Ever Lived?

Year	Population	Births per 1,000	Births Between Benchmarks	Number Ever Born	Percent of Those Ever Born
50,000 B.C.E.	2	–	–	–	–
8000 B.C.E.	5,000,000	80	1,137,789,769	1,137,789,769	0.4
1 C.E.	300,000,000	80	46,025,332,354	47,163,122,125	0.6
1200	450,000,000	60	26,591,343,000	73,754,465,125	0.6
1650	500,000,000	60	12,782,002,453	86,536,467,578	0.6
1750	795,000,000	50	3,171,931,513	89,708,399,091	0.9
1850	1,265,000,000	40	4,046,240,009	93,754,639,100	1.3
1900	1,656,000,000	40	2,900,237,856	96,654,876,956	1.7
1950	2,516,000,000	31-38	3,390,198,215	100,045,075,171	2.5
1995	5,760,000,000	31	5,427,305,000	105,472,380,171	5.5
2011	6,987,000,000	23	2,130,327,622	107,602,707,793	6.5
2017	7,536,000,000	19	867,982,322	108,470,690,115	6.9
2030	8,563,000,000	16	1,806,595,106	110,277,285,221	7.8
2050	9,846,000,000	15	2,833,529,982	113,110,815,203	8.7

Note: The estimates for those ever born apply only to live births; still births are not counted.

Source: Toshiko Kaneda and Genevieve Dupuis, 2017 World Population Data Sheet (Washington, DC: Population Reference Bureau, 2017); United Nations Population Division, World Population Prospects: The 2017 Revision (New York: United Nations, 2017).

там ещё довольно много текста