|In this thesis, we have discussed fuzzy sets, some properties and operations of fuzzy sets. t-norms and its generators are discussed briefly. Fuzzy numbers, types of fuzzy numbers, operations of fuzzy numbers and extension principle are also discussed. Elementary operations (addition, subtraction, multiplication and division) on L-R fuzzy numbers are presented with examples. Finally, we have presented exact calculation formulas for a t-norm-based addition of L-R fuzzy intervals. We have reviewed some research papers with proper references.