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

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The answer is explained here in detail!

Answer 2

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 $= \frac{5}{3}-\frac{5}{4}$

Profit on 1 disk $= \frac{5}{3}\cdot\frac{4}{4}-\frac{5}{4}\cdot\frac{3}{3}$

Profit on 1 disk $= \frac{20}{12}-\frac{15}{12}$

Profit on 1 disk $= \frac{5}{12}$

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

$\frac{100}{\left(\frac{5}{12}\right)} = 100\cdot\frac{12}{5} = 240$

Hence final answer is 240 disks.