Beacon Lesson Plan Library

50:50 Chances

Suzan Smith
Marion County Schools


This is the fifth lesson in the unit, Where We Come From. Students reinforce the probability of gender by using a coin toss, as they continue to search for the answers to genetics questions by using mathematical expectations of probability.


The student compares experimental results with mathematical expectations of probabilities.

The student determines odds for and odds against a given situation.


- Student copies of the 50:50 Chances worksheet and the Probability Questions with journal entry worksheet (See associated file)
- A teacher overhead of the 50:50 Chances worksheet
- 1 coin, a penny, per groups of 2 students


1. Make student copies of the 50:50 Chances worksheet and the Probability Questions with journal prompt for each student.
2. Create a teacher copy of the 50:50 Chances worksheet for the overhead.
3. Gather pennies for the students to flip.


1. After the previous lesson in the unit, Pair ‘Em Up!, the students have had experience with probability and Punnett Squares. As a warm up, ask the students to draw a Punnett Square predicting the probable outcome of gender. Work with them until it is correct. Also review and allow students to correct their answers on the Conclusion Questions worksheet they completed in the previous lesson plan. Since you will have already formatively assessed these, allow students to correct their answers to use in studying for the summative assessment at the end of the unit.

2. Remind the students that the Punnett Squares only provide a probable outcome, but that the actual outcomes can vary. Ask them how this can be.

3. Tell the students that today they are going to again test the accuracy of Punnett squares by using coin tosses to represent the gender outcomes of offspring in 15 families. Each of the 15 families will have 6 children, for a total of 90 children (90 coin tosses). Put students into groups of 2. Distribute the 50:50 Chances worksheet. Have the students predict how many of the children (flips) will be girls, and how many of their children (flips) will be boys. They should write this at the top of their worksheet.

4. Review and model the procedure and recording with the students.

5. Provide the students with the following instructions:
-- In this activity, heads = boy; tails = girl.
-- Flip your coin 6 times, keeping track of how many times you flip heads vs tails.
-- Record your total for each gender under Family 1 in the first Data Table.
-- Continue to flip the coin 6 more times for EACH family on the data table (14 more times). (Make sure the students understand that they are to flip 6 times for EACH family, them record.) Recommend that they use tally marks on a scratch piece of paper.

6. For Data Table 2, record the number of times each outcome was flipped for.

7. After all students have completed the toin coss and the tallying, pull students back together and ask them to compare their results with their predictions. Ask why the predictions and the results are different.Reinforce the concept that probability is just that....the probable outcome. Genetics can only predict, not assure, the outcome.

8. Distribute the Probability Questions worksheet and journal (short answer question) prompt. Allow time for students to work.


This activity is formatively assessed by completion of the 50:50 Chances worksheet, response to the Journal prompt, and thoughtful and complete answers to the Probability Questions worksheet. The 50:50 Chances worksheet and activity are group assessed and the journal and Probability Questions worksheet are individually assessed. Answer keys are provided in the associated file.


The Beacon Unit Plan associated with this lesson can be viewed by clicking on the link located at the top of this page or by using the following URL: Once you select the unit’s link, scroll to the bottom of the unit plan page to find the section, Associated Files. This section contains links to the Unit Plan Overview, Diagnostic and Summative Assessments, and other associated files (if any).
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