Problem 2. Marco thought of a number. He subtracted 12.12 from the number and divided the resulting difference by $\frac{1}{5}$. To the obtained result, he added 1.85 and then divided the sum by 0.1. This way, he got the number 68.5. What number did Marco think of?
Solution. First method. Let the guessed number be $x$. According to the condition of the problem, we have the equation

$$
\left((x-12.12): \frac{1}{5}+1.85\right): 0.1=68.5
$$

which solution is $x=13.12$. Therefore, Marko guessed the number 13.12.

Second method. The number 68.5 is obtained by dividing some number by 0.1, which means that before that Marko got the number $68.5 \cdot 0.1=6.85$. This number Marko got by adding the number 1.85, so the previous number is $6.85-1.85=5$. The number 5 is obtained by dividing the previous number by $\frac{1}{5}$, so the previous number is $5 \cdot \frac{1}{5}=1$. Finally, the number 1 is obtained when the guessed number is reduced by 12.12, so the guessed number is $1+12.12=13.12$.