Question posted by Corie from the United States:
Grade/Level: Grade 5
Question solved by Model Method: Stella has twice as many fish as Catherine. Catherine has twice as many fish as Rita. They have 70 fish altgether. How many fish does Rita have in her tank?
Step 1: This question involves the Repeated Variable Concept . Stella has twice as many fish as Catherine, so we draw 1 box to represent Catherine's fish and 2 boxes to represent Stella's fish.
Step 2: And since Catherine has twice as many fish as Rita, Rita should have only half as many fish as Catherine. We divide Catherine's model into 2 equal units and draw 1 unit to represent the number of fish Rita has.
Step 3: Next, we divide all the boxes of Stella's model into equal units to make all the unknown parts equal.
Step 4: As they have 70 fish altgether, we draw a bracket to the right to show that all the fish add up to 70.
From the model,
7 units ---------- 70 fish
1 unit ---------- 70 fish / 7 = 10 fish
Therefore, Rita has 10 fish in her tank.
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