Question 1206419
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The ratio of the price of a cassette to the price of a VCD was 1:5. Each VCD cost $25. 
On a certain day, the amount of money collected from the sale of both VCDs and cassettes was $6720. 
If the number of cassettes sold made up 1/5 of the total number of VCDs and cassettes sold, 
how many VCDs were sold on that day?
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<pre>
Each VCD costs $25.  Hence, each cassette costs  {{{(1/5)*25}}} = 5 dollars.


Let x be the number of cassette sold.  Then the number of VCD is 4x.


The total revenue equation is 

    5*x + 25*(4x) = 6720  dollars.


Simplify and find x

    5x + 100x = 6720

      105x    = 6720

         x    = 6720/105 = 64.


<U>ANSWER</U>.  64 cassettes and 4*64 = 256 VCDs were sold that day.
</pre>

Solved using one equation in one unknown.


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It also can be solved mentally using the grouping method,
without any equations.