AA batteries come in packs of 4. Last month, Joe used 58 batteries in his remote control drone. How many packs of batteries did he have to open?

Batteries come in a pack of 4.

This means

Number of batteries in each pack = 4.

Number of batteries Joe used last month for his remote controlled drone = 58.

Number of packets he needs to open = 58/4 = 14.5

But you cannot open half a packet.

So the number of packets we need to open to use 58 batteries is 15.