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At a stationery shop, the ratio of the number of blue pens to the number of red pens is 4:5. After 280 blue pens and 280 red pens were sold, the ratio of blue pens to the red pens became 9:20. How many pens were there at the stationery shop at

first?

 Oct 15, 2023
 #2
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Let b = initial number of blue pens and r = initial number of red pens.

 

Form the following two equations and solve them for r and b:

 

\(\frac{b}{r}=\frac{4}{5}\\ \frac{b-280}{r-280}=\frac{9}{20}\)

 Oct 17, 2023

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