If 5, 15, 3 and x are in proportion, then find the value of x.

Options

A. 9
B. 13
C. 7
D. none of these

Answer

To solve the problem where 5, 15, 3, and x are in proportion, we can follow these steps:

### Step 1: Understand the concept of proportion
When four numbers are in proportion, it means that the ratio of the first two numbers is equal to the ratio of the last two numbers. This can be expressed mathematically as:
\[ \frac{A}{B} = \frac{C}{D} \]
In our case, we have:
\[ \frac{5}{15} = \frac{3}{x} \]

### Step 2: Set up the equation
From the proportion, we can set up the equation:
\[ \frac{5}{15} = \frac{3}{x} \]

### Step 3: Cross-multiply
To eliminate the fractions, we can cross-multiply:
\[ 5 \cdot x = 15 \cdot 3 \]

### Step 4: Calculate the right side
Now, calculate the right side of the equation:
\[ 5x = 45 \]

### Step 5: Solve for x
To find the value of x, divide both sides by 5:
\[ x = \frac{45}{5} \]
\[ x = 9 \]

### Conclusion
Thus, the value of x is 9.