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No! Not by a long shot. With larger numbers, you cannot tell whether an odd number is prime or composite just by the last digits. All prime numbers greater than 7 must end in one or these: 1, 3, 7 or 9. But not all numbers ending with 1, 3, 7 or 9 are prime.

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Well for example 207 is divisible by 3 so the answer is no (207 is 69 times three). The simple test (ie to check for 3 as divisor or also called a factor) is to add all the individual numbers up (here it totals 9) and then if that number is divisible by three then you don't have a Prime number. So 27 is also not a prime - it divides by three. (quick check again the total of the numbers is 9 ie divisible by three) and another example 57 can be divided by 3 to give 19 and the quick check is 5 and 7 totals 12 which is then divisible by three.

ps don't forget you need to check for all the other numbers also! ie like 4, 5, 7, 9, 11, 13 ... etc

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Q: Are all numbers that end in seven all primes?
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