In each of the following question a question is asked followed by three information. You have to decide whether the question can be answered with any one or two or all thee three informations.
A train moving with a uniforms speed crosses a standing bus in 20 seconds. What is the speed of the train?
Information
(1)Length of the train
(2) Length of the bus
(3)speed of the bus

Options

A. If the information (1) and (2) are necessary
B. If the information (2) and (3) are necessary
C. If the information (1) (2) and (3) are necessary
D. None of these

Answer

To solve the problem, we need to determine the speed of a train that crosses a standing bus in 20 seconds. We have three pieces of information to consider:

1. Length of the train (L_train)
2. Length of the bus (L_bus)
3. Speed of the bus (S_bus)

### Step-by-Step Solution:

**Step 1: Understand the scenario.**
- The train is moving with a uniform speed and crosses a standing bus. The time taken to cross the bus is given as 20 seconds.

**Step 2: Identify what is needed to find the speed of the train.**
- The speed of the train can be calculated using the formula:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
- In this case, the distance covered by the train while crossing the bus is the sum of the lengths of the train and the bus:
\[ \text{Distance} = L_{\text{train}} + L_{\text{bus}} \]

**Step 3: Set up the equation using the given time.**
- The time taken to cross the bus is 20 seconds, so we can express the speed of the train as:
\[ \text{Speed of the train} = \frac{L_{\text{train}} + L_{\text{bus}}}{20} \]

**Step 4: Analyze the information provided.**
- **Information 1 (Length of the train)**: This is necessary to calculate the distance.
- **Information 2 (Length of the bus)**: This is also necessary to calculate the distance.
- **Information 3 (Speed of the bus)**: This is not necessary since the bus is standing still; its speed does not affect the calculation of the train's speed.

**Step 5: Conclusion.**
- To find the speed of the train, we need both the length of the train and the length of the bus. Therefore, we can conclude that:
- The question can be answered using **Information 1 and Information 2**.

### Final Answer:
The correct answer is that we need **Information 1 and Information 2** to determine the speed of the train.

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