Encyclopedias 83005

The seller sells books for 20 euros and encyclopedias for 50 euros. How many books and encyclopedias did he sell if he sold 121 books? He won €8,000 for both types.

Correct answer:

k =  -65
e =  186

Step-by-step explanation:

$$\begin{gathered} 20k+50e=8000 \\ k+e=121 \\ 20\cdot k+50\cdot e=8000 \\ k+e=121 \\ 50e+20k=8000 \\ e+k=121 \\ Row2-\frac{1}{50}\cdot Row1\to Row2 \\ 50e+20k=8000 \\ 0.6k=-39 \\ k=\frac{-39}{0.6}=-65 \\ e=\frac{8000-20k}{50}=\frac{8000-20\cdot (-65)}{50}=186 \\ e=186 \\ k=-65 \end{gathered}$$

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