Find the greatest 2-digit prime number.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 97
A prime number has no factors other than 1 and itself. Check the two-digit numbers downwards from 99; for a number below 100 it is enough to try the primes 2, 3, 5 and 7, because \(\sqrt{100}=10\).
99 \(=9\times11\), so it is not prime
98 is even, so it is not prime
97 is not divisible by 2, by 3 (digit sum 16), by 5, or by 7 (\(7\times13=91\), \(7\times14=98\)), so 97 is prime