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Missing question stem. Based on the provided images, the following numeric options are available:
71
31
91
61
91
Check divisibility by small primes (2, 3, 5, 7). For 91, remember that it is a famous composite number: 7×13=91.
Numbers to identify for primality: 71, 31, 91, 61.
p=a number with exactly two factors: 1 and itself
Check divisibility by small primes (2, 3, 5, 7). For 91, remember that it is a famous composite number: 7×13=91.
Many students mistake 91 for a prime number because it is not divisible by 2, 3, or 5, but it is actually 7×13.
Analyze 71
Check for divisibility by primes up to 71≈8.4. Factors to check: 2, 3, 5, 7. 71 is not divisible by 2 (odd), 3 (sum of digits 8), 5 (ends in 1), or 7 (7×10=70). Thus, 71 is prime.
71 is prime
Analyze 31
Check for divisibility by primes up to 31≈5.5. Factors to check: 2, 3, 5. 31 is not divisible by 2, 3, or 5. Thus, 31 is prime.
31 is prime
Analyze 91
Check for divisibility by primes up to 91≈9.5. Check divisibility by 7: 91÷7=13. Since 91 has factors 1, 7, 13, and 91, it is composite.
91=7×13
Analyze 61
Check for divisibility by primes up to 61≈7.8. Factors to check: 2, 3, 5, 7. 61 is not divisible by 2, 3, 5, or 7. Thus, 61 is prime.
61 is prime
C is correct because 91 is a composite number (7×13=91), whereas 71, 31, and 61 are all prime numbers.
Always verify numbers ending in 1 by checking the multiplier of 7 (e.g., 21, 51, 81, 91), as these are often composite despite appearing prime.
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