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.
It means Joe has to open 15 packets of batteries.
<u>Answer:</u>
96
<u>Step-by-step explanation:</u>
Let's assume that the marks needed in the next exam is 
. Then if the average becomes 90,
Now we can simply solve for :
⇒ 
⇒ 
[Multiplying both sides by 4]
⇒ 
[Subtracting 264 from both sides]
⇒ 
Therefore, you need to score 96 in your next exam to have an average of 90 on the four exams.
