Although large mammals like elephants and whales tend to live longer than small ones like mice, larger breeds of dogs...

Phase 1: Owning the Dataset

Visualization Selection

Since we're dealing with a relationship between body mass (continuous variable) and life span, let's use a number line to visualize the mass differences.

Body Mass Number Line:

|-------|-------|-------|-------|-------|------->
0       10      20      30      40      50     Mass (kg)
        ↑                ↑
   Reference        Our breed
   (10 kg)          (x kg)

Understanding the Relationship

The passage tells us: "for every 2 kilograms of body mass, life span is 1 month less"

This means:

• \(+2 \text{ kg body mass} \rightarrow -1 \text{ month life span}\)
• The relationship is: \(\text{Life span difference} = \frac{\text{Mass difference}}{2}\)

Phase 2: Understanding the Question

Breaking Down the Statement

The question states: "The average life span of a breed with an average body mass of x kg is y months less than the average life span of a breed with an average body mass of 10 kg."

This means:

• We have a reference breed: 10 kg
• We have another breed: x kg
• The x kg breed lives y months less than the 10 kg breed

Key Insight

Since the x kg breed lives LESS (fewer months), it must be HEAVIER than 10 kg. So \(x > 10\).

The formula becomes: \(y = \frac{x - 10}{2}\)

Phase 3: Finding the Answer

Systematic Calculation

We need both x and y to be in our choices: [10, 15, 20, 25, 30, 35]

Let's check each possible x value greater than 10:

If \(x = 15\): \(y = \frac{15 - 10}{2} = \frac{5}{2} = 2.5\) → Not in choices

If \(x = 20\): \(y = \frac{20 - 10}{2} = \frac{10}{2} = 5\) → Not in choices

If \(x = 25\): \(y = \frac{25 - 10}{2} = \frac{15}{2} = 7.5\) → Not in choices

If \(x = 30\): \(y = \frac{30 - 10}{2} = \frac{20}{2} = 10\) → Yes! 10 is in choices ✓

Stop here - we found our answer.

Verification

A breed with 30 kg average body mass would live 10 months less than a breed with 10 kg average body mass, which matches our relationship perfectly.

Phase 4: Solution

Final Answer:

• \(x = 30\)
• \(y = 10\)

The 30 kg breed lives 10 months less than the 10 kg breed, following the rule that every 2 kg increase in body mass corresponds to 1 month decrease in life span.