Final answer:
The expression for the total number of mangoes Nora bought is 6d, representing the 6 kilograms of mangoes she bought, multiplied by d, the number of mangoes per kilogram.
Step-by-step explanation:
The question asks for an expression to represent the total number of mangoes Nora bought. Since there are d mangoes in a kilogram, and Nora buys 4 kg initially and then 2 more kg, the total weight of mangoes bought is 4 kg + 2 kg = 6 kg. To find the total number of mangoes, we multiply the number of kilograms by the number of mangoes per kilogram, resulting in the expression 6d.
In the context of the provided examples, if we focus on addition and significant figures, we should remember that when we perform operations involving additions like in the case of buying fruits in different units, we should convert them all to the same unit and then add them up, ensuring to keep the precision consistent with the least precise measurement. However, in the mangoes scenario, we deal with a direct multiplication which does not involve significant figures or different measurements.