Sea Monkey Task – Facilitator Notes
Goals - Mathematics in the Task
The purpose of this task and exploration is for participants to be involved in
devising and executing statistical methods for problem solving in a real context.
Brine shrimp can be easily hatched and raised and they are abundant in the
Great Salt Lake (GSL). This task prompts individuals to devise a method for
counting living brine shrimp. Counting a sample and scaling is one strategy that
will be implemented.
Launch: Ask participants to discuss: What do we mean by randomness? Prior to
this prompt Bryna told a story about a friend showing up at the same movie she
was at and the friend said, “how random” yet was it really random when they
have similar tastes in movies they like. Chart their ideas. A random variable is
_______________.
Distribute the Sea Monkey task sheet. Ask a participant to read the prompt aloud
and then have some individual think time on the counting task. Remind people
that the brine shrimp are actually moving, that sometimes it is difficult to tell how
many shrimp are in clusters, and that catching and labeling the little guys could
be quite tricky. Ask participants to share with a partner their ideas for how to
count the brine shrimp. If they stop at one idea prompt them to thing of other
ways.(5-10 min monitor, don’t let it got too long) Have a whole group discussion
asking groups to share some ideas popcorn style.
Possible strategies include –
- photographing the dish and then counting piece by piece,
- catching and marking the counted ones,
- taking each shrimp out of the dish one-by-one,
- or counting shrimp in a particular sub-region of the circle and scaling.
Raise the issue of variation in the counting if it doesn’t come up on its own and
ask participants, “How can we increase the accuracy of our estimation?” Taking
multiple counts of shrimp within a particular region and averaging the result may
help. Through a leading discussion develop and post a procedure.
An Example:
1. Choose two regions equidistant from the center of the Petri dish.
2. Assign group roles as follows: 2 counters, 1 recorder, 1 timer
3. Every 10 seconds the timer calls time, the counters quickly make a count
of the number of shrimp in their region, and the recorder writes down the
counts.
4. Collect data for 1-minute worth of observations.
5. Average the counts to get an approximation for the number of shrimp in 1
such region.
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6. Compute the appropriate scale factor to scale the area of the chosen
region to the area of the entire dish.
7. Multiply the average by the scale factor.
Discuss this method with the participants and what is important for this method to
work. (The shrimp should be roughly uniformly distributed in the dish.)
Explore:
Give participants time to implement the counting method they devised and the
method above with a Petri dish and some real brine shrimp. Alternative methods
may include photographing and counting, using a smaller portion of a square grid
sheet rather than the polar graphing paper provided, etc… They should fill their
Petri dish with a small amount of the GSL water and then use a pipette to take a
bunch of brine shrimp and put them in their dish. Each group should then
proceed with the counting procedure.
Supplies needed for each group:
 Stopwatch
 Data collection sheet
 Markers
 A small plastic Petri dish
 A plastic pipette or eye-dropper with a .4mm opening using scissors to cut
the tip if necessary (see below)
 A coffee stirrer
Circulate and monitor the work progress of individual groups. Ask each person
to record important information in their procedure and their final resulting
estimation in their composition book.
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Discuss:
Ask participants for a summary of what they think was important about the
procedure. What did you attend to when counting your sea monkeys and how do
you know your estimation is reasonably accurate?
In the context of predicting the sea monkey population in a Petri dish, how can
we use statistical methods to make estimates?
Participants will potentially:

surface ideas such as . . .
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invent strategies to . . .
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random sample (what pieces did you use, did the sea monkeys move in
the same direction?) vs. representative sample
Mean, median, mode for different samples
Number of samples taken
area of samples same size
proportionality (to project for the whole Petri dish)
estimation of total population and error in the estimation
make estimation of the overall quantity within a whole geometric region
based on samples from a sub region
determine amount of error in the estimation
create representations that . . .
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facilitate the collection and recording data possibly through tables
Connect the chosen geometrical regions to the entire Petri dish using
fractions or geometric diagrams
Create an equation of proportional (a proportion)
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