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Tide-Pool Photos: Models and Field Results

Build uniform probability models for tide-pool photo surveys, calculate event probabilities, and explain differences from observed frequencies.

Grade 7MathInteractive · Printable

Aligned to7.SP.C.7.a

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What’s included

Single worksheet
Auto-graded online
1 Common Core standard
Printable answer key
14 questions
Classroom-ready

Details

Format: Interactive · Printable
Grade: Grade 7
Subject: Math
Question types: Fill in the blank, Multiple choice, Matching, Short answer

About this worksheet

What students practice

Students build uniform probability models using equally likely photo selections.
Students find event probabilities by counting favorable outcomes.
Students compare model probabilities with observed frequencies and explain random variation.

How to use

Have students use the photo inventory for Section 1 and the trial record for Section 2. Discuss why equally likely photos need not produce equally likely crab counts.

Curriculum

Common Core standard covered

7.SP.C.7.a

Build a uniform probability model, where every outcome is equally likely, use it to find probabilities, and compare probabilities from a model to observed frequencies and explain differences.

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Name Date

Tide-Pool Photos: Models and Field Results

Build equally likely models and compare predictions with observed results.

Build the Photo Model

A marine biology field-trip group photographs ten tide-pool squares. Use the inventory below for questions 1–5. Write probabilities as fractions or decimals.

Tide-Pool Photo Inventory
Photo number	Crabs visible	Snails visible
1	0	3
2	2	1
3	1	2
4	0	4
5	3	0
6	1	2
7	0	1
8	2	0
9	0	3
10	1	2

The group wants every photo number to be equally likely. Which procedure creates a uniform probability model?

A. Choose the photo with the greatest number of snails.
B. Use a random generator that gives each number 1–10 an equal chance.
C. Use a random generator that gives photo 1 twice the chance of each other photo.
D. Ask each student to choose a favorite photo number.