If any two numbers Highest Common Factor is 1, then they are called co-prime to each other.
HCF of 12 and 15 is 3
HCF of 7 and 15 is 1
HCF of 22 and 48 is 2
HCF of 24 and 36 is 12
Therefore 7, 15 is a pair of co-prime numbers since they have an HCF of 1.

Prime factorization is finding the factors of a number that are all prime. The prime factors of 15 are 3 and 5.

$9=3\times 3$
$\Rightarrow$ 9 is a multiple of 3
Hence any multiple of 9 will also be a multiple of 3.

The smallest factor of any number is 1 and the highest factor of any number is the number itself.
Therefore, the difference between the highest and the smallest factor of 100 is, $100-1=99$

Number of books = 72
Number of shelves = 8
Therefore, books on each shelf = 72 divided by 8  = 9

To get multiples of any number, we multiply counting numbers with that number.
Since there are infinite counting numbers, multiples of any number are also infinite.

HCF of two numbers $\times$ LCM of two numbers = Product of the two numbers
$12\times LCM=228$
LCM $=\frac{228}{12}=19$

The least number that is exactly divisible by 15, 10 and 16 is the LCM of the three numbers.

$\begin{array}{cc}2& 15,10,16\\ 2& 15,5,8\\ 2& 15,5,4\\ 2& 15,5,2\\ 3& 15,5,1\\ 5& 5,5,1\\ & 1,1,1\end{array}$
LCM of 15, 10 and 16 $=2\times 2\times 2\times 2\times 3\times 5=240$

First five prime numbers are: 2, 3, 5, 7, 11
Product of first five prime numbers is $2+3+5+7+11=28$