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# Ratios

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John has US and foreign stamps in his album. The ratio of the number of US stamps to foreign stamps is 5 : 2. After Paul gives him 12 foreign stamps, the ratio becomes 2 : 1. Find the number of US stamps he has.

Jun 6, 2021

#1
+208
+1

d=number of domestic stamps

f=number of foreign stamps

$$\:\frac{d}{f}=\frac{5}{2}$$

$$2d=5f$$

$$\frac{d}{f+12}=\frac{2}{1}$$

$$d=2f+24$$

substitute d in first equation:

$$2(2f+24)=5f$$

$$f=48$$

$$d=120$$

JP

Jun 6, 2021

#1
+208
+1

d=number of domestic stamps

f=number of foreign stamps

$$\:\frac{d}{f}=\frac{5}{2}$$

$$2d=5f$$

$$\frac{d}{f+12}=\frac{2}{1}$$

$$d=2f+24$$

substitute d in first equation:

$$2(2f+24)=5f$$

$$f=48$$

$$d=120$$

JP

JKP1234567890 Jun 6, 2021