Evdokimov M.A.

Last year, Misha bought a smartphone that cost a whole four-digit number of rubles. Visiting the store this year, he noticed that the price of the smartphone had increased by $20 \%$ and now consists of the same digits but in reverse order. How much did Misha spend on the smartphone?
Let Misha spent $\overline{a b c d}$ rubles on a smartphone ( $a, b, c, d$ - digits, and $a \neq 0$ and $d \neq 0$ ). By the condition $6 \overline{a b c d}$ $=5 \overline{d c b a}$. The right side is divisible by 5, so $d=5$. It is clear that the digit $a-$ is even and less than the digit $d$. On the other hand, $a+1 \geq 5 / 6 d>4$, therefore, $a=4$ and

$6(4000+100 b+10 c+5)=5(5000+100 c+10 b+4)$. From this, $550 b-440 c=990,5 b-4 c=9$, or $5(b-1)=4(c+$ 1). Therefore, $b=5, c=4$ or $b=9, c=9$.

## Answer

4545 rubles or 4995 rubles.