A bakery opened with its daily supply of 40 dozen rolls. Half of the rolls were sold by noon and 60% of the remaining rolls were sold between noon and closing time. How many dozen rolls were left unsold ?

Answer: Option B

Number of rolls sold by noon = $$\frac{1}{2}$$ of 40 dozen = 20 dozen
Number of rolls sold between noon and closing time :
= 60% of 20 dozen
= $$\left(\frac{60}{100}\times 20\right)$$   dozen
= 12 dozen
Number of rolls left unsold :
= [40 - (20 + 12)] dozen
= 8 dozen