instead of buying packages of 20 batteries for $7.00 to power his video game controllers, Nathaniel decides to buy 4 rechargeable batteries and a charger for $15.39. How many times does he need to use the rechargeable batteries to make them a better value?

Answer 1

If he buys x packs of batteries, we wan to find out how many packs it takes to cost more than the price of the charger and batteries.

7x > 15.39
x > 2.2

So, after using the rechargeable batteries 40 times, they will be the better buy.