225
Пошаговое объяснение:
Петров решил, что восьмерка - первая цифра кода. Осталось проверить 100 комбинаций вторых 2 цифр, кроме тех, в которых обе они четные. Исходим из того, что нуль - четное число/цифра. Таких комбинаций 25, их можно перечислить все:
00, 02, 04, 06, 08,
20, 22, 24, 26, 28,
40, 42, 44, 46, 48,
60, 62, 64, 66, 68,
80, 82, 84, 86, 88.
Значит, ему следует проверить оставшиеся 75 вариантов. Замок не открылся.
Петров решил, что восьмерка - вторая цифра кода. Проверил те же 75 комбинаций вторых 2 цифр - замок не открылся.
Петров решил, что восьмерка - третья цифра кода. Проверил те же 75 комбинаций вторых 2 цифр - замок открылся на последней 75+75+75=225-й попытке.
After my hard and busy school year my summer holidays began. I felt happy and began to plan a lot of wonderful things to do during my summer vacation.
I was dreaming about far South countries I always wanted to visit but I had to go to the Azove seaside with my relatives. The water was very warm there because you know Azove Sea isn’t deep. What I liked there - a lot of different kinds of entertainment there: "water mountains", water scooters and discos.
There was nothing to do all day except lying in the sun and getting a wonderful tan. I was playing with my little sister on the sand and in the waves teaching her to swim. Later I returned to Kherson and spent some time in town going out with my friends, reading, listening to music, watching TV, playing computer games. After that I went to the sports camp where I spent seven days.
It was very useful experience because I had to get up very early, to train a lot, and to rest very little. But it made me stronger and healthier.
I was very happy to return home and I spent several days in my summer cottage, I helped my grandpa to dig the garden, to water plants, and to gather fruit and vegetables. I was fishing with my grandpa and we were cooking fish together. Only insects were spoiling my good mood. I enjoyed floating by boat, swimming in the river and helping my grandparents.
During my summer holidays I made many new friends, read a lot of interesting books, got to know a lot of useful things. Now I feel ready to get back to school.
I am happy to meet my friends and teachers.
Чуть чуть можешь переделать)