Question

An unknown number is doubled and added to 50 to get 100. Which of the following is the unknown number?

• A. 20
• B. 25
• C. 50
• D. 10

Answer 1

The correct option is B 25

$\text{Let the unknown number be}x$.

Step 1: The number is doubled,
$\text{So, the new number will be = 2}x$

Step 2: The number is added to 50
$\text{So, the new number will be = 2}x\text{+ 50}$

Step 3: Equate this expression to 100.
$2x+50=100$

Step 4: Let's solve for $x$
Subtract 50 from both the sides
$2x+50-50=100-50$
$2x+0=50(\because 50-50=0;100-50=50)$
$2x=50$
$x=\frac{50}{2}(\because \text{bring 2 as a reciprocal to RHS}$
$x=25$
Hence, the unknown number is 25.