Akopyan A.V.

Through a terminal, money can be transferred to a mobile phone, with a commission of a natural number of percent. Fedya put an integer amount of rubles on his mobile phone, and his account was credited with 847 rubles. How much money did Fedya put on the account, given that the commission is less than $30\%$?
Let Fedia put $n$ rubles, and the commission is $k \%$. Then $(1-k / 100) n=847$, that is, $84700=$ $(100-k) n .84700=2 \cdot 2 \cdot 5 \cdot 5 \cdot 7 \cdot 11 \cdot 11$. According to the condition $70<100-k<100$, so it is necessary to find all numbers,
dividing 84700, in this range. A small enumeration shows that the only suitable option -

is $7 \cdot 11=77$, so $k=23$. Thus, Fedia put $n=87700: 77=1100$ rubles on the phone.

## Answer

1100 rubles.