GCF or HCF = Greatest Common Factor or Highest Common Factor LCM= Lowest Common Multiple. GCF : To understand GCF I illustrate an example. Suppose we need to calculate the GCF of two numbers of 16 and 18 , then first we write the factors of each number as tabulated below. Numbers                     Factors 16 1 2 4 8 16 18 1 2 3 6 9 18 Therefore we can define that the factor which is the greatest one and also common among the numbers are the GCF of those numbers. In the above two rows related to 16 and 18 we notice that 1 and 2 factors are common in the two numbers. But 2 is the greatest common factor. Therefore 2 is the GCF of  16 and 18.  Let us take another example. This is tabulated below. The common factors of 36 and 48 are 1,2,3,4,and 12. But 12 is the greatest one. Therefore GCF of 36 and 48 is 12.  Numbers

Unitary Method is that in which for further calculation value of unit (1) is required for further calculation. Unit means one,  mathematically '1'. A, An or Per also  mean  '1'. If we know the value of one then to find value of many we do MULTIPLICATION . Read this problem and the table. Problem 1: Cost of one mango is $ 4. Find the cost of 8 mangoes. - One Many 1 8 $ 4 ? Solution:  As the Cost of 1 mango is $ 4.  Therefor the cost of 8 mangoes is 8x4 = $ 32 Also Watch solution in the video given at the bottom . If we know the value of many then to find value of one we do DIVISION . Read this problem. Problem 2: Cost of one mango is $ 4. Find the cost of 8 mangoes. - Many One 8 1 $ 40 ? Solution:  As the Cost of 8 mango is $ 40.  Therefor the cost of 1 mango is 40/8 = $ 5 Also Watch solution in the video  given at the bottom . If we know the value of many then to find