What Does 'of' Mean in Algebra?

The word ‘of’ in algebra is used in expressions involving fractions, ratios, and percentages. It is used to find a part of something. The word ‘of’ refers to multiplying numbers. The word ‘of’ in a indicates multiplication. 
Example: 1/2 of 10.
The 1/2 of 10 refers to multiplying 1/2 by 10. 
1/2 × 10 = 5.
 

In word problems, the word ‘of’ indicates that multiplication is required to find part of a quantity. It is used to find the part of a whole. 
For example, Emilin read 3/5 of a 20-page book. Calculate the total number of pages Emilin read. 
Here the 3/5 of 20 refers to 3/5  × 20 = 3 × 4 = 12.

Lilly has 60 chocolates, and she gave 1/3 of them to her friend. How many chocolates did Lilly give to her friend?
Here, it is mentioned that Lilly gave 1/3 of 60 chocolates to her friend. Therefore, we have to multiply 1/3 by 60 to find the total number of chocolates Lilly gave to her friend.
1/3 × 60 = 20
Therefore, Lilly gave 20 chocolates to her friend.