Question

Rolex buys computer disks at a price of 4 for $5 and sells them at a price of 3 for $5. How many computer disks must he sell to make a profit of $100

Answer 1

Given that Rolex buys computer disks at a price of 4 for $5 .

That means cost price of 1 disk = 5/4

Given that Rolex sells them at a price of 3 for $5.

That means selling price of 1 disk = 5/3

Profit on 1 disk = selling price - cost price

Profit on 1 disk
`= (5)/(3)-(5)/(4)`

Profit on 1 disk
`= (5)/(3)\cdot(4)/(4)-(5)/(4)\cdot(3)/(3)`

Profit on 1 disk
`= (20)/(12)-(15)/(12)`

Profit on 1 disk
`= (5)/(12)`

Now we have to find how many disk to be sold to get the profit $100

so we just divide $100 by profit on 1 disk

`(100)/(\left((5)/(12)\right)) = 100\cdot(12)/(5) = 240`

Hence final answer is 240 disks.