Grade 1 · Count a collection once · 39 of 750
Count a collection once: objects in the collection: 16
At a classroom activity, 16 counters are arranged with up to 3 in each display row. Find the original count, explain the calculation, and check a related question.
Try the question, use a hint when you need one, and compare your reasoning with the worked solution. The animation starts with this chapter’s values; changing its controls explores a new case.
01 · Make a prediction
Your practice question
At a classroom activity, 16 counters are arranged with up to 3 in each display row. First find the original count. Then answer: One more counter is added to the original collection. What is the new count?
Use this scratch space or work on paper. Your notes stay on this page and clear when you leave. Answers are for self-checking; they are not automatically graded.
A starting point
Match exactly one counting word to each object. An incomplete row still belongs to the collection, and changing the row length does not change the total.
Work through the reasoning
Step 1
Identify the quantities and the task
At a classroom activity, 16 counters are arranged with up to 3 in each display row. The first task is to find the original count. Match exactly one counting word to each object. An incomplete row still belongs to the collection, and changing the row length does not change the total.
Step 2
Calculate the original result
Counted + not yet counted = total. The starting collection has 16 objects regardless of whether a row holds 3 or another allowed count.
Step 3
Complete the follow-up calculation
One more counter is added to the original collection. What is the new count? 16 + 1 = 17 objects. The original objects remain and one new object joins them.
The answer
Counted + not yet counted = total. The starting collection has 16 objects regardless of whether a row holds 3 or another allowed count. Follow-up: 16 + 1 = 17 objects. The original objects remain and one new object joins them.
Compare the method as well as the result. A different valid method may reach the same answer. Keep exact values until the last step when the question asks for rounding.
02 · Explore the model
See the mathematical relationship move.
Use Play, Pause, and the timeline to inspect the construction. Reset restores the question’s original settings. The displayed assumptions describe where this model applies.
Watch the relationship
PausedHD animation studio
From experiment to screen.
Present a crisp Canvas scene, save a full-HD image, or capture your model as a silent video.
The mathematical idea
At a classroom activity, 16 counters are arranged with up to 3 in each display row. Match exactly one counting word to each object. An incomplete row still belongs to the collection, and changing the row length does not change the total. The starting collection has 16 objects regardless of whether a row holds 3 or another allowed count.
Counted + not yet counted = total
03 · Reflect and transfer
Explain what changes and why.
Move the timeline to color each object once; stop before the end and account for the pale objects too. Explain which quantity changes and which relationship stays valid. Use the starting values again before checking your written answer.
This is a distinct guided scenario using a reusable mathematical model. Similar-looking diagrams can represent different given values and conclusions; they are not different mathematical theories.