Someone asks if 27 is a prime number. Tanvi says yes, because 27 is odd — it's not divisible by 2

Why

Tanvi's check is a real and useful first step — ruling out 2 does eliminate half of all numbers instantly, since none of them can be prime if they're even (except 2 itself). Where it goes wrong is stopping there, as if failing to divide by 2 is proof of nothing else dividing either. Try dividing 27 by other small numbers: 27 ÷ 3 = 9 exactly, with no remainder. That means 27 has at least three factors — 1, 3, and 27 — which is already one more than a prime is allowed to have. So 27 is NOT prime; it's composite, built from 3 × 9 (or 3 × 3 × 3). Checking "divisible by 2" tells you whether a number is even, nothing more — to know if a number is prime you have to test it against every smaller number that could divide it, not just the most common one. Rohan is right: one clean division isn't enough to call a number prime.