standard_description: Relate counting to addition and subtraction (e.g., by counting on 2 to add 2).
problem_activity: Below is an illustration of an aquarium. There are four possibilities of changes that affect the water level: addition/removal of a rock, insertion/removal of a plug, turn on/off the faucet, use the bucket to add/remove water.
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The graph below shows the height of the water in the aquarium over a 17-minute time interval. Write a story from the point of view of someone watching what is going on with the aquarium to produce the given graph.
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The graph given above is a simplified version of reality. What simplifying assumptions did we make when we created the graph?


aligns: no