Problem 7.2. Vlad and Dima decided to earn some money. Each of them decided to deposit 3000 rubles in the bank and withdraw all the money after a year.

Vlad chose the deposit "Confidence": the amount increases by $20\%$ over the year, but the bank charges a $10\%$ fee upon withdrawal.

Dima chose the deposit "Reliability": the amount increases by $40\%$ over the year, but the bank charges a $20\%$ fee upon withdrawal.

("The bank charges a fee of $n\%$" means that the bank keeps $n\%$ of the current deposit amount and returns the remaining part to the owner.)

Who will receive a higher annual profit from the deposit?

What will the difference be? Express the answer in rubles. If the profit is the same, write 0.
Answer: Dima will earn 120 rubles more.

Solution. Vlad's deposit amount will increase to $3000 \cdot 1.2$ rubles in a year, and after withdrawal, it will decrease to $3000 \cdot 1.2 \cdot 0.9=3240$ rubles.

Dima's deposit amount will increase to $3000 \cdot 1.4$ rubles in a year, and after withdrawal, it will decrease to $3000 \cdot 1.4 \cdot 0.8=3360$ rubles.

Therefore, Dima will earn 120 rubles more.