Problem 21. (8 points)

Dmitry's parents decided to buy him a laptop for his birthday. They calculated that they could save the required amount in two ways. In the first case, they need to save one-tenth of their salary for six months. In the second case, they need to save half of their salary for one month, and then deposit it in the bank for ten months at $3\%$ per month (calculated using simple interest). In the first case, the money will be just enough for the laptop, while in the second case, after buying the laptop, there will be some money left, which will be enough to buy a computer desk for 2875 rubles. What is the mother's salary, if the father's salary is 30% higher? (Provide the answer as a whole number, without spaces or units of measurement.)
Answer: 25000.

## Comment:

Solution:

Mom's salary is $x$, then dad's salary is $1.3x$. We set up the equation:

$(x + 1.3x) / 10 \times 6 = (x + 1.3x) / 2 \times (1 + 0.03 \times 10) - 2875$
$1.38x = 1.495x - 2875$

$x = 25000$