Answer:
Assuming 16 and 17. 5 books in 5 shelves, do you need help making an array? for 17, composite since you can divide the new number by either prime number, and a prime number can only be divided by 1 and itself.
Step-by-step explanation:
What are the prime numbers in between 21 and 30?
Well all numbers are 21, 22,23,24, 25, 26, 27, 28, 29, 30.
We know right away prime numbers can't be even so now we have 21, 23, 25, 27, 29.
Fives are easy to check for too so we can get rid of 25.
21, 23, 27, 29. Now it's pretty easy to check each one for being prime. the prime numbers are 23 and 29. Now, it says taking 4 away means it can be divided up, or another way to say that is taking 4 away beams the new number won't be prime. taking 4 away gives us 19 and 25. Well we know one is definitely not prime, and if you check you can see the other one is. So 25 is our answer.
the only way 25 splits up is 5x5, so that means there are 5 books per shelf and 5 shelfs.
for 17 the defenition of prime is that it can only be divided by 1 and itself. If you multiply two different numbers to get a new number, then this new number can be dived by the two you used. For example 3 and 2 multiply to get 6. Because of that you can divide 6 by 2 to get 3 or divide 6 by 3 to get 2, so since it is divisible by more than just 1 and itself, it is not prime. Let me know if you need any more help with this.
