Four chocolates

Marek wanted to buy four chocolates but was short of 30 cents. So he bought three chocolates and chewing gum for twenty cents, and he still had 70 cents left. How much did the chocolate cost? How much did Marek have?

Correct answer:

c =  1.2 eur
m =  4.5 eur

Step-by-step explanation:

$$\begin{gathered} m=4c-0.30 \\ m=3c+0.20+0.70 \\ 4c-0.30=3c+0.20+0.70 \\ 4\cdot c-0.30=3\cdot c+0.20+0.70 \\ c=1.2 \\ c=\frac{1.2}{1}=1.2 \\ c=\frac{6}{5}=1.2=1.2\text{eur} \end{gathered}$$

$m=4\cdot c-0.30=4\cdot 1.2-0.30=4.5\text{eur}$

Try another example