If a sum deposited at compound interest be- comes double in 4 years, when will it be 4 times at the same rate of interest ?

Answer

To solve the problem of determining how long it will take for a sum of money deposited at compound interest to quadruple (become four times) when it is known that it doubles in 4 years, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Problem**:
- We know that a certain principal amount (let's denote it as P) doubles in 4 years. This means that after 4 years, the amount becomes 2P.

2. **Finding the Time to Quadruple**:
- To find out when the amount will become 4 times the original principal (4P), we can use the fact that if the amount doubles in a certain time, it will double again in the same amount of time.
- Since the amount doubles in 4 years, we can say:
- After 4 years: Amount = 2P
- After another 4 years (total of 8 years): Amount = 2P × 2 = 4P

3. **Conclusion**:
- Thus, it will take a total of 8 years for the original amount to quadruple.

### Final Answer:
The sum will be 4 times in **8 years**.

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