Explanation: To understand the concept of successive discounts, let's consider an example where an article originally costs \( P \) rupees. The first discount is 30%, and the second discount is 40%.
1. **First Discount Calculation:**
- The first discount is 30%, so the price after the first discount is:
\[
P_1 = P - 0.30P = 0.70P
\]
- This means the price is reduced to 70% of the original price.
2. **Second Discount Calculation:**
- The second discount is 40%, but it is applied to the new price \( P_1 \):
\[
P_2 = P_1 - 0.40P_1 = 0.60P_1
\]
- Substituting \( P_1 \) from the first step:
\[
P_2 = 0.60 \times 0.70P = 0.42P
\]
- This means the final price is 42% of the original price.
3. **Total Discount Calculation:**
- The total discount is the difference between the original price and the final price:
\[
\text{Total Discount} = P - P_2 = P - 0.42P = 0.58P
\]
- This means the total discount is 58% of the original price.
Therefore, the total discount when two successive discounts of 30% and 40% are applied is 58%. This is why option D is the correct answer.
It is important to note that the total discount is not simply the sum of the individual discounts (30% + 40% = 70%) because the second discount is applied to the reduced price after the first discount, not the original price. This compounding effect is a key concept in understanding successive discounts.