1. The problem asks for the sum of integers from 1 to 15. 2. We use the formula for the sum of the first $n$ natural numbers: $$S = \frac{n(n+1)}{2}$$ where $n=15$. 3. Substitute $n=15$ into the formula: $$S = \frac{15 \times (15+1)}{2} = \frac{15 \times 16}{2}$$. 4. Calculate the multiplication: $$15 \times 16 = 240$$. 5. Divide by 2: $$\frac{240}{2} = 120$$. 6. Therefore, the sum of integers from 1 to 15 is $120$. This formula works because pairing numbers from the start and end (1+15, 2+14, etc.) each sum to the same value, simplifying the addition process.