Question

Make six prime numbers using the digits 1, 2, 3, 4, 5, 6, 7, 8, 9 once each.

Answer 1

Answer:

2, 3, 5, 7, 11, 13.

Step-by-step explanation:

A prime number is a number that you don't get a whole number when divided by 2 but you do get a whole number when divided by prime numbers such as 3,5,7,11... Basically a number with two factors, it can only be divided by 1 or themselves. for example:

9/2 = 4.5 (this is not a whole number so it might be a prime.

9/3 = 3 (it works when divided by a prime number.

another:

8/2 = 4 (it gives a whole number when divided by 2 therefor, it can't be a prime number.

Answering:

There are 6 prime numbers at the top^^^^.

Answer 2

One possible answer is  2, 3, 5, 41, 67, 89

Another possible answer is  2, 3, 5, 47, 61, 89

Other answers may be possible.

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Explanation:

This is a trial and error type of problem. Though with practice it's not as blind of randomly guessing.

We have 9 values here. If we paired them up, then we can form at most 4 pairs (since 9/2 = 4.5 rounds down to 4). That means we won't be able to form six two-digit primes. Some of the primes must be single digits.

We can have 3 single digit primes and 3 two-digit primes since 3+2*3 = 9.

The single digit primes are: 2, 3, 5, 7

Let's say 2 and 5 are definitely locked down to be the single digit group. I'm doing this since we can't have 2 or 5 as the units digit. If the units digit is 2, then 2 is a factor and it's not prime. Similarly, if 5 is the units digit, then 5 is a factor and that two digit value is not prime.

For good measure, we'll throw 3 in there as well and see what happens.

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The digits we have left are: 1, 4, 6, 7, 8, 9

The number 14 isn't prime, but 41 is prime

67 is prime so that's another two values off the list

lastly, 89 is prime so that works as well.

So one possible sequence is 2, 3, 5, 41, 67, 89

Notice how we can swap the 1 and 7 to go from 41,67 to 47,61; this gets us two other primes. So another possible answer is 2, 3, 5, 47, 61, 89

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Side note: having the list of primes on a reference sheet is a handy recommendation. You only need to go up as high as 97 which is the largest two digit prime.