3.1.1 Using an Area Model

​Can you bend your thumb backwards at the middle joint?

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​Can you roll your tongue into a "U" shape?

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​There are special genes that allow you to be able to do either one of these things.

​Assume that half the U.S. population can bend their thumbs backwards, and half can roll their tongues.

​Also assume that these genes are independent (having one gene does not affect whether or not you have the other) and randomly distributed (spread out) throughout the population.

​This table is useful because every cell in the table is equally likely. Therefore, each possible outcome has a 1/4 probability.

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​In reality, however, only 1/4 of the population can bend their thumb, and 7/10 can roll their tongue. Draw a new table to represent these new probabilities.

​You and your best friend may not only look different, you may also have different types of blood! For instance, members of the American Navajo population can be classified into two groups (73% has type O blood, while 27% has type A blood.

​(Blood types describe certain chemicals, called antigens, that are found in a person's blood).

​COPY THIS TABLE AND COMPLETE IT.

​Zack and Nick (both from Vermont) are shipwrecked on a desert island! Zack has been injured and is losing blood rapidly, and Nick is the only person around to give him a transfusion.

​Most populations can be classified into four blood types: O (45%), A (40%), B (11%), AB (4%). These percentages are based on Vermont populations.

​Copy and complete this area model on your own paper. If the outside probabilities are percentages, then the inside needs to be percentages as well.