Institution: Bangladesh Development Bank Exam: Bangladesh Development Bank Ltd - Senior Officer - 24.11.2017
Topic: Arithmetic Mathematics (পাটিগণিত), Subject: Mathematics (সাধারণ গণিত)

Best Answer Explained in Below-:

To determine how long it will take the train to pass a 650-meter long platform, we first need to calculate the train's speed. The train, which is 240 meters long, takes 24 seconds to pass a pole.

The speed of the train can be calculated as follows:

\[
\text{Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{240 \, \text{meters}}{24 \, \text{seconds}} = 10 \, \text{meters per second}
\]

Next, when the train passes a platform, it must cover both the length of the train and the length of the platform. Therefore, the total distance to be covered is:

\[
\text{Total Distance} = \text{Length of Train} + \text{Length of Platform} = 240 \, \text{meters} + 650 \, \text{meters} = 890 \, \text{meters}
\]

Now, we can calculate the time taken to pass the platform using the formula for time:

\[
\text{Time} = \frac{\text{Total Distance}}{\text{Speed}} = \frac{890 \, \text{meters}}{10 \, \text{meters per second}} = 89 \, \text{seconds}
\]

Thus, the time taken for the train to completely pass the 650-meter long platform is 89 seconds, which corresponds to option B.