If leonard bought 2 packs of batteries for x amount of dollars, how many packs of batteries could he purchase for $5.00 at the same rate?

2 pack of batteries cost x dollars.
Therefore 1 pack of batteries costs x/2 dollars

Let n packs of batteries be purchased for $5.00
Then 1 pack of batteries costs 5/n dollars

Equate the cost of 1 pack of batteries.
x/2 = 5/n
Cross multiply.
nx = 10
n = 10/x

The number of packs of batteries is 10/x.