What should come in place of the question mark (?) in the following questions ?
` ? % of 280 + 18% of 550 = 143.8`

Options

A. 11
B. 18
C. 21
D. 16

Answer

To solve the equation \( ?\% \text{ of } 280 + 18\% \text{ of } 550 = 143.8 \), we will follow these steps:

### Step 1: Convert the percentage into a decimal
Let \( x \) be the value that replaces the question mark. The equation can be rewritten as:
\[ \frac{x}{100} \times 280 + \frac{18}{100} \times 550 = 143.8 \]

### Step 2: Calculate \( 18\% \text{ of } 550 \)
First, we calculate \( 18\% \text{ of } 550 \):
\[ \frac{18}{100} \times 550 = 0.18 \times 550 = 99 \]

### Step 3: Substitute the value back into the equation
Now, substitute \( 99 \) back into the equation:
\[ \frac{x}{100} \times 280 + 99 = 143.8 \]

### Step 4: Isolate the term with \( x \)
Subtract \( 99 \) from both sides:
\[ \frac{x}{100} \times 280 = 143.8 - 99 \]
\[ \frac{x}{100} \times 280 = 44.8 \]

### Step 5: Solve for \( x \)
Now, multiply both sides by \( 100 \) to eliminate the fraction:
\[ x \times 280 = 44.8 \times 100 \]
\[ x \times 280 = 4480 \]

Now, divide both sides by \( 280 \):
\[ x = \frac{4480}{280} \]

### Step 6: Simplify the fraction
Calculating \( \frac{4480}{280} \):
\[ x = 16 \]

### Conclusion
Thus, the value that should come in place of the question mark is \( 16 \).

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