The fourth proportional to 4,7 and 20 is

Options

A. 28
B. 21
C. 18
D. 35

Answer

To find the fourth proportional to the numbers 4, 7, and 20, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Fourth Proportional**:
The fourth proportional to three numbers \( a, b, c \) is a number \( x \) such that the ratio \( a:b = c:x \).

2. **Set Up the Proportion**:
Here, we have the numbers 4, 7, and 20. We need to find \( x \) such that:
\[ \frac{4}{7} = \frac{20}{x} \]

3. **Cross-Multiply**:
To solve for \( x \), we can cross-multiply:
\[ 4 \cdot x = 7 \cdot 20 \]

4. **Calculate the Right Side**:
Now, calculate \( 7 \cdot 20 \):
\[ 7 \cdot 20 = 140 \]
So, we have:
\[ 4x = 140 \]

5. **Solve for \( x \)**:
To find \( x \), divide both sides by 4:
\[ x = \frac{140}{4} \]
Simplifying this gives:
\[ x = 35 \]

6. **Conclusion**:
Therefore, the fourth proportional to 4, 7, and 20 is:
\[ \boxed{35} \]