Given:

LCM of two prime number x and y is 161

where x > y

Concept:

Prime number: 

• The numbers other than 1 whose only factors are 1 and the number itself are called Prime numbers.
• 2 is the smallest prime number which is even.
• Every prime number except 2 is odd.

The least common multiple (LCM): 

• It is the “smallest non-zero common number” which is a multiple of both the numbers.
• For example, consider two numbers x and y, whose prime factors are,

x = a × a × b × c

y = a × b × b × b 

Then,

LCM of x and y will be = a × a × b × b × b × c

Calculation:

Prime factors of 161 are 7 and 23 only. Therefore we can say that LCM of 7 and 23 will be 161.

Hence, we can write,

161 = 7 × 23 

Hence,

x = 23 and y = 7 (as x > y)

Now the value of 3y - x is

3 × 7 - 23 = -2

Hence, the value of 3y -x is -2.

Composite number: 

• Numbers having more than two factors are called Composite numbers.
• 1 is neither a prime nor a composite number.
• Two numbers having only 1 as a common factor are called co-prime numbers.

Highest Common Factor:

• The Highest Common Factor (HCF) of two or more given numbers is the highest of their common factors.
• The product of the HCF and LCM of two numbers is equal to the product of the two numbers.​