Explanation:

- To find the equivalent single discount, we apply each successive discount on the reduced price from the previous step.

- First discount of 30% on 100 leaves 70% of the price: $100\times (1-0.30)=70$.

- Second discount of 25% on the new price: $70\times (1-0.25)=52.5$.

- Third discount of 15% on the latest price: $52.5\times (1-0.15)=44.625$.

- The final price is 44.625% of the original, meaning a total discount of $100-44.625=55.375$.

Therefore, the equivalent single discount is:

Option 2: 55.375%