Rule: write the decimal as a mixed number. Whole part + fraction from the decimal part.

Rule: simplify the fraction by dividing numerator and denominator by their HCF.

Decimal	=	2.75
The whole number part is 2. The decimal part 0.75 = 75/100. So 2.75 = 2 75/100.
Find the HCF of 75 and 100. 75 = 25 x 3, 100 = 25 x 4. HCF = 25.
Simplify fraction	=	75/100 = (75 / 25)/(100 / 25) = 3/4
Mixed number	=	2 3/4
2 3/4 matches option (1).