Imagine an HIV test that is 95% accurate (false positive rate of 5%) and around 2% of the tested population is infected with HIV. What is the probability that you actually have HIV when your test comes back positive?
He was born on February 29th in a leap year. Consequently, in his 87 years, he only witnessed twenty-one of his actual birthdays. The other years there was no February 29th.
During WWII, there was a bridge connecting Germany and Switzerland, and on the German side, there was a sentry tower with a guard in it. He would come out every three minutes to check on the bridge, and he had orders to turn back anyone who tried to get into Germany, and shoot anyone trying to escape without a pass. There was a woman who desperately needed to get into Switzerland, and she knew she didn’t have time to get a pass. It would take her at least six minutes to cross the bridge, but she managed to do it. How?
She walked on the bridge towards Switzerland for 3 minutes and just as the guard was about to come out, she turned around walking back to Germany. The guard saw her and asked for her pass but she didn’t have one and was sent back (or what the guard thought was back) to Switzerland. In her case it was the very country she wanted to go to.
Noon and midnight are both 12 o’clock and the Twelve Days of Christmas is a popular Christmas carol.
There are twelve face cards in a standard 52-card deck and twelve is the largest number with one syllable.
There are twelve steps in Alcoholics Anonymous, a troy pound is 12 ounces, there were 12 tribes of Israel and a popular movie was called, “Twelve Angry Men” (12 members of the jury). There are twelve function keys on your keyboard. F1 often shows a help screen and F5 reloads pages in your browser.
Many recipes measure items by the dozen, adding one more for a baker’s dozen. There are twelve months in a year.
It’s surprising how many times the number twelve shows up in our culture.