Together 81384

Soňa and Elvíra have 20 CZK together, Elvira and Filoména have 15 CZK together, and Sonia and Filoména have 19 CZK together.
How many CZK does Soňa have, how much Elvira, and how much Filomena?

Correct answer:

s =  12
e =  8
f =  7

Step-by-step explanation:

$$\begin{gathered} s+e=20 \\ e+f=15 \\ s+f=19 \\ e+s=20 \\ e+f=15 \\ f+s=19 \\ Row2-Row1\to Row2 \\ e+s=20 \\ f-s=-5 \\ f+s=19 \\ Row3-Row2\to Row3 \\ e+s=20 \\ f-s=-5 \\ 2s=24 \\ s=\frac{24}{2}=12 \\ f=-5+s=-5+12=7 \\ e=20-s=20-12=8 \\ e=8 \\ f=7 \\ s=12 \end{gathered}$$

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