Question 105738
List all the prime numbers between 55-75. I am confused about Prime Numbers, exactly what are they in plain ole english could someone please explain. Thanks, Zack


Let's think it SO SIMPLY. prime numbers are numbers that can only be divided by one. Take an example, like 7. Do you know any numbers other than 1 and 7 that is divided by? no. there is no such number. But if you take 4, which is composite, you have more than just 1 and 4. it's also 2.

Also, ALL even numbers are composite. It is so because even numbers can be divided by 2.
Any number that ends with 0 or 5 is composite. they are divisible by 5.


So let's go from 55-75:

55) Nope. 55 can also be by 5 and 11. Let's skip 55,60,65,60 and 75. they are divisible by 5.
56) Even. so no.
57) You might think 57 is prime, but there is a special way to know if this is a prime or composite: use a good old-fashioned 3 divisible tricks: Add the each digit of the number up, so in here, 5 and 7. If the number added is divisible by 3, then it is divisible by 3. So 5 + 7 = 12. 12 can be divided by 3 evenly, yes? so this is not prime.
58) Even. (Let's skip 60,62,64,66,68,70,72 and 74. they're all evens.
59) Yes! this is a prime number, because 59 can only be divided by 1 and 59.
61) Yes! this is a prime number, because 61 can only be divided by 1 and 61.
63) Not a chance. 9 times 7 is 63.
67) Yes! this is a prime number, because 67 can only be divided by 1 and 67.
69) Nope. Remember 3 fivisible trick? 6 + 9 = 15, and 15 is divisible by 3.
71) Yes! this is a prime number, because 71 can only be divided by 1 and 71.
73) Yes! this is a prime number, because 73 can only be divided by 1 and 73.

So the following list is:
59,61,67,71,73

Alright. Good luck.