Institution: Bangladesh Bank Exam: অফিসার (ক্যাশ ) - Sonali | Rupali | BD Krishi | Rajshahi Krishi Unnayn | Investment Corporation Of Bangladesh - ২৯. ০৩.২০১৯ ||
Topic: Arithmetic Mathematics (পাটিগণিত), Subject: Mathematics (সাধারণ গণিত)

Best Answer Explained in Below-:

To understand when the man will successfully climb the 11 m wall, we need to analyze his climbing pattern. He climbs 1 meter each minute but slips back 50 cm (0.5 m) after each minute. Therefore, his effective climbing height each minute can be calculated as follows:

- After climbing 1 m and slipping 0.5 m, his net gain each minute is:

\( 1 \, \text{m} - 0.5 \, \text{m} = 0.5 \, \text{m} \)

Now, let’s calculate how long it takes him to get close to the top. After 20 minutes, his progress would be:

- At 20 minutes, his total effective climb is:

\( 20 \, \text{minutes} \times 0.5 \, \text{m/min} = 10 \, \text{m} \)

At this point, while he has climbed to 10 m, he has not yet reached the top of the 11 m wall. However, in the 21st minute, he climbs 1 m up to 11 m, successfully reaching the top without slipping back because he finishes the climb at that moment.

Thus, he completes his climb at:

- 5:00 pm + 21 minutes = 5:21 pm

This confirms that the correct answer is option C: 5:21 pm.