To calculate the circumference of a circle, Mack would use the formula:

$C = 2\pi r$

where $C$ is the circumference, and $r$ is the radius of the circle. For this problem, the radius $r = 7$ cm. Thus, the formula would become:

$C = 2\pi(7) = 14\pi \text{ cm}$

Now, let's categorize the calculations based on whether they would give the correct result for the circumference:

1. Correct Calculation:

   • $2\pi \times 7$
   • Explanation: This directly applies the formula for circumference.

2. Incorrect Calculation:

   • $\pi \times 7^2$
   • Explanation: This is the formula for the area of a circle, not the circumference.

3. Incorrect Calculation:

   • $\pi \times 14$
   • Explanation: This formula doesn't follow the circumference formula; it uses the diameter (14 cm), but it’s not multiplying by 2.

4. Incorrect Calculation:

   • $7^2$
   • Explanation: This only calculates the square of the radius, which is part of the area formula but not related to the circumference.

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Do you want more details or have any other questions about this?

Here are 5 related questions to help expand on this topic:

1. What is the formula for calculating the area of a circle?
2. How would you calculate the circumference if the diameter was given instead of the radius?
3. How can the relationship between diameter and radius be used to simplify circumference calculations?
4. If the radius was 5 cm, how would the calculations change for the circumference?
5. What is the value of $\pi$ to use for practical approximations?

Tip: Always ensure that the right formula is being used for the specific property you're calculating—circumference, area, or something else!