The beaver family have three mobile phones but none of the batteries have any charge. It takes 1 hour to fully charge a mobile phone but this does not need to be done all in one go. The beaver family only have two mobile phone chargers in the house.
Question:
What is the shortest time they need to fully recharge the three phones?
Option:
a. 3 hours
b. 2 hours
c. 1.5 hours
d. 1 hour
The answer is d. 1.5 hour, here is the explanation:
The charging can be achieved in the following way: 1. charge mobile 1 + 2 for half an hour. 2. charge mobile 1 + 3 for half an hour. 3. charge mobile 2 + 3 for half an hour. Also, we cannot charge the phones in less than 1 hour and a half. Indeed, we need to cumulatively charge for three hours. We have two chargers, therefore we can only do it twice as fast at most, that is in 1 hour and a half.
Confuse? Lets see the visualisation to make it easier!
https://scratch.mit.edu/projects/179837702/
