To solve this, we can model the problem with an array that represents how much Randy saves each week, and determine how many weeks it takes for him to reach $21.

Understanding the problem:

• Randy saves $7 per week.
• He wants to save a total of $21.
• We need to find how many weeks it takes to reach $21.

Now, let's break it down in terms of savings per week:

• After Week 1: $7 saved
• After Week 2: $7 + $7 = $14 saved
• After Week 3: $7 + $7 + $7 = $21 saved

Thus, it takes 3 weeks to save $21. The array representing the savings per week would be:

$[7, 14, 21]$

Each element in this array corresponds to Randy’s cumulative savings after each week.

Would you like further details or have any questions? Here are 5 related questions for deeper understanding:

1. How can you express this problem as a multiplication equation?
2. What is the relationship between the total amount saved and the number of weeks?
3. What would happen if Randy saved $5 per week instead of $7? How many weeks would it take?
4. If Randy wanted to save $35, how many weeks would it take at $7 per week?
5. What other strategies could Randy use to save money faster?

Tip: When dealing with problems involving equal groups, arrays can visually represent cumulative totals, helping to solve multiplication problems easily.