{"id":421,"date":"2011-10-31T17:04:25","date_gmt":"2011-10-31T09:04:25","guid":{"rendered":"http:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/?p=421"},"modified":"2024-02-16T21:13:34","modified_gmt":"2024-02-16T13:13:34","slug":"7-billion","status":"publish","type":"post","link":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/2011\/10\/7-billion\/","title":{"rendered":"7 Billion"},"content":{"rendered":"<p>According to <a href=\"http:\/\/www.unfpa.org\/public\/op\/edit\/home\/news\/pid\/8691\" target=\"_blank\" rel=\"noopener\">official sources<\/a>, the world&#8217;s 7 billionth person was born today. This is a fiction. The goal is to raise awareness about the world&#8217;s population. It&#8217;s working &#8211; the news seems to be <a href=\"http:\/\/timharford.com\/2011\/10\/malthuss-ghost-and-baby-number-7bn\/\" target=\"_blank\" rel=\"noopener\">all over<\/a> <a href=\"http:\/\/www.thebigquestions.com\/2011\/10\/31\/happy-birthday-baby-seven-billion\/\" target=\"_blank\" rel=\"noopener\">the blogosphere<\/a>.<\/p>\n<p><!--more-->Part of the reason for the fiction is that we don&#8217;t have good enough information about populations to be sure what exact day &#8211; or even year &#8211; the world&#8217;s population will pass 7 billion. Counting people, even in developed countries or totalitarian regimes &#8211; is tricky.<\/p>\n<p>Another reason is that there may not be a unique 7 billionth person. After all, the population is not increasing steadily. It increases by 1 every time someone&#8217;s born, and jumps back down every time someone dies.<\/p>\n<p><strong>On average<\/strong>, there&#8217;s<\/p>\n<ul>\n<li>4.40 births every second, that is, one birth every 0.227 seconds,<\/li>\n<li>1.84 deaths every second, or one every 0.543 seconds, that is,<\/li>\n<li>The population of the world changes 6.24 times every second. Each time it changes, the chance that it went up is about 7 in 10, and the chance it went down is 3 in 10.<\/li>\n<\/ul>\n<p>Imagine that in the instant just passed, the 7 billionth child was born. The only way he or she could be the unique 7 billionth child (instead of just one of the several) is if<\/p>\n<ul>\n<li>the next population change was a birth (only a 7 in 10 chance)<\/li>\n<li>the one after that is also a birth (another 7 in 10 chance)<\/li>\n<li>beyond that, there are never enough deaths to outweigh the births and bring the population back to 7 billion.<\/li>\n<\/ul>\n<p>The chance of just the first two conditions happening is only 7\/10 x 7\/10, or just under 50%. The exact probability that there&#8217;s be only 1 unique 7 billionth child can be worked out with a bit of complicated algebra, using the theory of what are called &#8220;Markov Chains&#8221;. The chance that there will be only one 7 billionth child is in fact about 3 in 7, or 43%. There&#8217;s a 57% chance that there&#8217;ll be more than one.<\/p>\n<p>If more than one, then how many?<\/p>\n<p>This is, fortunately, a bit easier to work out. We don&#8217;t need Markov Chains any more. Just imagine that the 7 billionth child has just been born. The chance that there&#8217;ll be no more 7 billionth children is 43%. However, this is the same, whether or not the child just born is the first, second, fifth or 100th &#8220;7 billionth child&#8221;.<\/p>\n<p>Therefore,<\/p>\n<ul>\n<li>The chance that there&#8217;s a unique 7 billionth child is 3\/7, or 43%.<\/li>\n<li>The chance that there will be exactly two of them is 4\/7 x 3\/7 = 12\/49, or 24%.<\/li>\n<li>The chance there will be exactly three of them is 4\/7 x 4\/7 x 3\/7, or 14%.<\/li>\n<li>The chance that there will be exactly four is 4\/7 x 4\/7 x 4\/7 x 3\/7, or 8%.<\/li>\n<li>The chance that there will be exactly five is 4.6%, and the chance there will be five or more &#8220;7 billionth children&#8221; is just under 11%.<\/li>\n<li>The average of all these is that we should expect about 2.33 kids to be able to claim the title of Seven Billionth Human.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>According to official sources, the world&#8217;s 7 billionth person was born today. This is a fiction. The goal is to raise awareness about the world&#8217;s population. It&#8217;s working &#8211; the news seems to be all over the blogosphere.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[81],"tags":[311,310,108],"_links":{"self":[{"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/posts\/421"}],"collection":[{"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/comments?post=421"}],"version-history":[{"count":2,"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/posts\/421\/revisions"}],"predecessor-version":[{"id":1363,"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/posts\/421\/revisions\/1363"}],"wp:attachment":[{"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/media?parent=421"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/categories?post=421"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.dr-mikes-math-games-for-kids.com\/blog\/wp-json\/wp\/v2\/tags?post=421"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}