1. The problem states that the masses of flour, butter, and sugar in shortbread biscuits are in the ratio 4 : 3 : 2 respectively. 2. To find the fraction of the shortbread biscuit made up of sugar, first find the total parts of the ratio: $$4 + 3 + 2 = 9$$ 3. The fraction of sugar in the biscuit is the part of sugar over the total parts: $$\frac{2}{9}$$ 4. Therefore, the fraction of the shortbread biscuit that is sugar is $\frac{2}{9}$.