Cement, sand, and gravel are mixed in the ratio `1:2:3`, respectively, to make concrete. What percentages of cement, sand, and gravel are used in concrete?

Answer

To find the percentages of cement, sand, and gravel used in concrete, we start with the given ratio of the materials, which is 1:2:3.

### Step-by-Step Solution:

1. **Identify the parts in the ratio**:
- Cement = 1 part
- Sand = 2 parts
- Gravel = 3 parts

2. **Calculate the total parts**:
\[ \text{Total parts} = 1 + 2 + 3 = 6 \]

3. **Calculate the percentage of cement**:
\[ \text{Percentage of Cement} = \left(\frac{\text{Cement part}}{\text{Total parts}}\right) \times 100 = \left(\frac{1}{6}\right) \times 100 \approx 16.67\% \]

4. **Calculate the percentage of sand**:
\[ \text{Percentage of Sand} = \left(\frac{\text{Sand part}}{\text{Total parts}}\right) \times 100 = \left(\frac{2}{6}\right) \times 100 \approx 33.33\% \]

5. **Calculate the percentage of gravel**:
\[ \text{Percentage of Gravel} = \left(\frac{\text{Gravel part}}{\text{Total parts}}\right) \times 100 = \left(\frac{3}{6}\right) \times 100 = 50\% \]

### Final Results:
- Percentage of Cement: **16.67%**
- Percentage of Sand: **33.33%**
- Percentage of Gravel: **50%**