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In most industrialized countries about 105 boys are born for every 100 girls, for a ratio of 1.05,
known as the secondary sex ratio, or SSR; the primary sex ratio is the ratio at conception.
This is often expressed as the percentage of boys among all births, or about 51.2 percent.
The source:
https://www.scientificamerican.com/article/is-a-pregnant-womans-chan/#:~:text=In%20most%20industrialized%20countries%20about,births%2C%20or%20about%2051.2%20percent.
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It is a typical example of experimental probability.