A boy was asked to multiply a certain number by 50.He multiplied it by 30 and got his answer less then the correct one by 400.The number to be multiplied was:

Options

A. 10
B. 20
C. 30
D. 40

Answer

To solve the problem step by step, let's denote the unknown number as \( x \).

1. **Understanding the Problem**: The boy was supposed to multiply the number \( x \) by 50, which gives \( 50x \). However, he mistakenly multiplied it by 30, resulting in \( 30x \). The difference between the correct answer and his answer is given as 400.

2. **Setting Up the Equation**: According to the problem, we can express the difference mathematically:
\[ 50x - 30x = 400 \]

3. **Simplifying the Equation**: Now, simplify the left side of the equation:
\[ 20x = 400 \]

4. **Solving for \( x \)**: To find the value of \( x \), divide both sides of the equation by 20:
\[ x = \frac{400}{20} \]

5. **Calculating the Result**: Performing the division gives:
\[ x = 20 \]

Thus, the number to be multiplied was **20**.