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Worksheet 1 Coin Flipping Activity
Let’s check if the coin in our pocket is fair or biased!
1. What is the null hypothesis?
______________________________________________________________
______________________________________________________________
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2. Take a quarter and flip it 20 times, recording the number of heads and tails:
Number of heads
Number of tails
3. What is the expected number of heads and tails, assuming that it is equally
likely to get heads and tails?
Expected number of heads
Expected number of tails
4. Calculate the difference between observed (first table) and expected
(second table) number of heads and tails:
Observed number of heads - expected
number of heads
Observed number of tails - expected
number of tails
5. Square the obtained numbers:
(Observed number of heads - expected
number of heads)2
(Observed number of tails - expected
number of tails)2
6. Divide the number by the expected number of heads or tails:
(Observed number of heads - expected
number of heads)2 / expected number of
heads
(Observed number of tails - expected
number of tails)2 / expected number of
tails
7. Now add the two numbers together; this is chi square!
chi square = ______________________
Is the obtained number greater or less than 3.84?
**3.84 is a cutoff that tells you whether the difference you observe is
significant or if it happens by chance. Chi squares greater than 3.84 are
significant. Chi squares less than 3.84 are not significant (the difference
happens randomly/by chance).
8. Is your coin fair or biased?
Worksheet 2 Colony Activity
Let’s check if the substance you tested during the last lab is a mutagen!
1. What is the null hypothesis?
______________________________________________________________
______________________________________________________________
______________________________________________________________
2. Count the number of colonies on your control part of the plate and the part
with the substance tested (coffee, mascara, shampoo, etc.):
Observed number of colonies in control
Observed number of colonies in test
3. What is the expected number of colonies in the control and the test,
assuming that the yeast are equally likely to grow on either side?
Note that this number will be the same for the test and the control and will be
½ of all the colonies that you’ve counted (for example, if you count 40 total
colonies on your test and your control sections, the number will be ½ of 40 =
20 colonies).
Expected number of colonies in control
Expected number of colonies in test
4. Calculate the difference between observed (first table) and expected
(second table) number of colonies:
Observed number of colonies in control expected number of colonies in control
Observed number of colonies in test expected number of colonies in test
5. Square the obtained numbers:
(Observed number of colonies in control expected number of colonies in control)2
(Observed number of colonies in test expected number of colonies in test)2
6. Divide the number by the expected number of colonies:
(Observed number of colonies in control expected number of colonies in control)2 /
expected number of colonies in control
(Observed number of colonies in test expected number of colonies in test)2 /
expected number of colonies in test
7. Now add the two numbers together; this is chi square!
chi square = ______________________
Is the obtained number greater or less than 3.84?
**3.84 is a cutoff that tells you whether the difference you observe is
significant or if it happens by chance. Chi squares greater than 3.84 are
significant. Chi squares less than 3.84 are not significant (the difference
happens randomly/by chance).
8. Can your substance cause mutations in yeast?