Apptitude - Number System

 Concepts

• Multiples and Factors
• Total no. of factors of a composite number
• LCM & HCF
• Co-prime Numbers
• Unit Digit
• Highest power of P in n!
• Concepts of Remainder
• Divisibility

Co-Prime Numbers: 

Co-prime numbers are two numbers that have no other common factor than one. A set of co-prime numbers should consist of at minimum two numbers. Co-prime numbers, for example, {4 and 7}, {5, 7, 9} and 9, have just 1 as their greatest common factor. Co-prime numbers do not always have to be prime numbers.

Highest Common Factors (H.C.F) or greatest common Divisor (G.C.D) 
 two or more than two numbers is the greatest number that divides each one of them exactly. 

 Eg: H.C.F of 8 & 20 is 4 

Lowest Common Multiple (L.C.M): 

 The least number which is exactly divisible by each of them given numbers is called their lowest common multiple (L.C.M) 

 Eg: L.C.M of 8 & 20 is 40

Relation between L.C.M and H.C.F. of two Numbers:

 LCM X HCF = Product of the two numbers