IB Bio Year 1
Chi Square Problem Set
2 =  (O-E) 2 / E
Directions: Please work these problems out in your journal, showing all work! This means: state the null
hypothesis, calculate the 2 test statistic, compare the 2 test statistic to the appropriate 2 critical value in a
table of 2 probabilities (easy to find online) and accept or reject your null
hypothesis.
1. In a series of crosses (matings) involving different color phases in
domesticated minks, a U. of Wisconsin biologist obtained: 53 dark, 17
platinum, 24 aleutian, and 8 sapphire minks. He had expected a color
ratio of 9 dark : 3 platinum : 3 aleutian : 1 sapphire. Do the biologist’s
data “fit” the expected ratio?
2. According to Wikipedia, the following are approximate frequencies of the various ABO blood
types in the USA population: 40% Type A, 11% Type B, 4% Type AB, and 45% Type O. In the
town of Podunk, NY there are 178 persons with A blood, 34 with B blood, 11 with AB blood, and
225 with O blood. (Ok I made that last part up.) Are the blood type data from Podunk representative of
the USA?
3. A new surgical technique is tried on 30 patients with a disease that normally is 50% fatal.
Twenty-two of the thirty patients survive the disease. Is the new surgical technique effective?
IB Bio Year 1
Chi Square Problem Set
2 =  (O-E) 2 / E
Directions: Please work these problems out in your journal, showing all work! This means: state the null
hypothesis, calculate the 2 test statistic, compare the 2 test statistic to the appropriate 2 critical value in a
table of 2 probabilities (easy to find online) and accept or reject your null
hypothesis.
1. In a series of crosses (matings) involving different color phases in
domesticated minks, a U. of Wisconsin biologist obtained: 53 dark, 17
platinum, 24 aleutian, and 8 sapphire minks. He had expected a color
ratio of 9 dark : 3 platinum : 3 aleutian : 1 sapphire. Do the biologist’s
data “fit” the expected ratio?
2. According to Wikipedia, the following are approximate frequencies of the various ABO blood
types in the USA population: 40% Type A, 11% Type B, 4% Type AB, and 45% Type O. In the
town of Podunk, NY there are 178 persons with A blood, 34 with B blood, 11 with AB blood, and
225 with O blood. (Ok I made that last part up.) Are the blood type data from Podunk representative of
the USA?
3. A new surgical technique is tried on 30 patients with a disease that normally is 50% fatal.
Twenty-two of the thirty patients survive the disease. Is the new surgical technique effective?