It is given that batteries come in a packs of 4. It means in each pack there are 4 batteries.
Joe used 58 batteries . So to find the total number of packets of batteries joe has to open is
Number of batteries used / Total number of batteries in each packet
= 58 / 4
= 14.5
The number of battery can not be in decimal. So we will round the answer to integer. If we round it to 14 it means 14 packets. But in 14 packets there are 14*4 = 56 batteries .
But we know that Joe used 58 batteries. So we will round the final answer to 15.
