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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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Each VCD costs $25. Hence, each cassette costs = 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.
ANSWER. 64 cassettes and 4*64 = 256 VCDs were sold that day.
Solved using one equation in one unknown.
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It also can be solved mentally using the grouping method,
without any equations.