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An integer \(\mathrm{n}\) that is greater than 1 is said to be "prime-saturated" if it has no prime factor greater than or equal to \(\sqrt{\mathrm{n}}\). Which of the following integers is prime saturated?
Let's break down what "prime-saturated" means in everyday language. Think of it this way: imagine you have a number, and you want to check if it's "prime-saturated." You need to do two things:
If all prime factors are strictly less than \(\sqrt{n}\), then the number is prime-saturated. If even one prime factor is greater than or equal to \(\sqrt{n}\), then it's NOT prime-saturated.
Process Skill: TRANSLATE - Converting the mathematical definition into checkable stepsLet's find the square root of each answer choice. This gives us the "threshold" that all prime factors must stay below:
Now we know exactly what each number's prime factors need to be smaller than.
Let's break down each number into its prime factors:
Now we have everything we need to test each option.
Let's check each option systematically by comparing every prime factor to the square root threshold:
Option A) 6: Prime factors are 2 and 3, threshold is \(\sqrt{6} \approx 2.45\)
- Is \(2 < 2.45\)? ✓ Yes
- Is \(3 < 2.45\)? ✗ No (\(3 > 2.45\))
Not prime-saturated.
Option B) 35: Prime factors are 5 and 7, threshold is \(\sqrt{35} \approx 5.92\)
- Is \(5 < 5.92\)? ✓ Yes
- Is \(7 < 5.92\)? ✗ No (\(7 > 5.92\))
Not prime-saturated.
Option C) 46: Prime factors are 2 and 23, threshold is \(\sqrt{46} \approx 6.78\)
- Is \(2 < 6.78\)? ✓ Yes
- Is \(23 < 6.78\)? ✗ No (\(23 > 6.78\))
Not prime-saturated.
Option D) 66: Prime factors are 2, 3, and 11, threshold is \(\sqrt{66} \approx 8.12\)
- Is \(2 < 8.12\)? ✓ Yes
- Is \(3 < 8.12\)? ✓ Yes
- Is \(11 < 8.12\)? ✗ No (\(11 > 8.12\))
Not prime-saturated.
Option E) 75: Prime factors are 3 and 5, threshold is \(\sqrt{75} \approx 8.66\)
- Is \(3 < 8.66\)? ✓ Yes
- Is \(5 < 8.66\)? ✓ Yes
All prime factors are less than the threshold! This IS prime-saturated.
The answer is E) 75.
\(75 = 3 \times 5 \times 5\), and both prime factors (3 and 5) are strictly less than \(\sqrt{75} \approx 8.66\), making it the only prime-saturated number among the choices.
1. Misunderstanding "greater than or equal to": Students often miss that the definition says "no prime factor greater than or equal to \(\sqrt{n}\)" which means ALL prime factors must be STRICTLY LESS than \(\sqrt{n}\). They might incorrectly think a prime factor can equal \(\sqrt{n}\) and still satisfy the condition.
2. Confusing the direction of comparison: Students may flip the inequality and think they need to find numbers where prime factors are greater than \(\sqrt{n}\) instead of less than \(\sqrt{n}\), completely reversing the prime-saturated condition.
3. Misinterpreting what constitutes a prime factor: Students might include composite factors or forget that repeated prime factors (like 5 appearing twice in \(75 = 3 \times 5^2\)) only need to be checked once since we only care about distinct prime factors.
1. Prime factorization errors: Students often make mistakes when breaking down numbers into prime factors, especially for numbers like \(46 = 2 \times 23\) where they might not recognize that 23 is prime, or incorrectly factorize 75 as something other than \(3 \times 5^2\).
2. Square root calculation mistakes: Students may incorrectly estimate square roots, particularly for numbers like \(\sqrt{35} \approx 5.92\) or \(\sqrt{75} \approx 8.66\), leading to wrong threshold values for comparison.
3. Incomplete checking: Students might check only some prime factors against the square root threshold but forget to verify ALL prime factors, especially when a number has multiple prime factors like \(66 = 2 \times 3 \times 11\).
1. Stopping at the first "close" answer: Students might find that option A) or B) seems to work without carefully checking all calculations, and select it without verifying all five options systematically.
2. Boundary confusion: When a prime factor is very close to the square root threshold (like checking if \(7 < 5.92\)), students might incorrectly conclude it satisfies the condition due to hasty comparison or rounding errors.