A device needs 4 batteries to run. Each battery runs for 2 days. If there are a total of 6 batteries available, what is the maximum number of days for which the device can be run by strategically replacing the batteries till all the batteries are completely drained of power?

Correct option is B

Given:

• Each battery lasts 2 days.
• The device needs 4 batteries to run.
• Total batteries = 6.

Formula:
Maximum runtime = Total battery-days ÷ 4 (number of batteries used at once).

Solution:

1. Each battery lasts for 2 days, so total battery-days:
   6 × 2 = 12 battery-days
2. Divide the total battery-days by the number of batteries required at once:
   Maximum runtime = 12 ÷ 4 = 3 days

Final Answer: (b) 3