Grandma 12

Tobias wanted to buy a five-part series of books about hockey. Each book in the series costs the same amount. But he only had 80% of the price for the first and second volumes. Grandma paid him the rest for the first and second volumes and 60% of the price for the third volume. Dad paid the remaining amount of 1,200 CZK. How much CZK did Grandma pay in total?

Final Answer:

x =  342.8571

Step-by-step explanation:

$$\begin{gathered} 5a=0.80\cdot 2\cdot a+0.60\cdot a+1200 \\ 5\cdot a=0.80\cdot 2\cdot a+0.60\cdot a+1200 \\ 2.8a=1200 \\ a=\frac{1200}{2.8}=428.57142857 \\ a=\frac{3000}{7}\doteq 428.571429 \\ x=0.20\cdot a+0.60\cdot a=0.20\cdot 428.5714+0.60\cdot 428.5714=342.8571 \end{gathered}$$

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