Alex invested his savings in two parts. The simple interest earned on the first part at 15% per annum for 4 years is the same as the simple interest earned on the second part at 12% per annum for 3 years. Then, the percentage of his savings invested in the first part is:

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To solve this problem:

1. **Let the Investments Be**:  
   Let Alex invest $$ x $$ in the first part and $$ y $$ in the second part.

2. **Simple Interest Formula**:  
   Simple Interest = Principal × Rate × Time.

3. **Interest Earned on Each Part**:  
   - For the first part:  
     $$ 	ext{SI}_1 = x 	imes 0.15 	imes 4 = 0.6x $$
   - For the second part:  
     $$ 	ext{SI}_2 = y 	imes 0.12 	imes 3 = 0.36y $$

4. **Equating Interests**:  
   Since the simple interest earned on both parts is equal:  
   $$
   0.6x = 0.36y
   $$  
   Simplify to find the ratio of $$ x $$ to $$ y $$:  
   $$
   \frac{x}{y} = \frac{36}{60} = \frac{3}{5}.
   $$

5. **Total Investment**:  
   The total investment is:  
   $$
   x + y.
   $$

6. **Percentage of Savings in First Part**:  
   The percentage of savings invested in the first part is:  
   $$
   \frac{x}{x + y} 	imes 100 = \frac{3}{3 + 5} 	imes 100 = \frac{3}{8} 	imes 100 = 37.5\%.
   $$

Thus, Alex invested **37.5%** of his savings in the first part.

Answer

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