NOIP preliminary round some of the topics
NOIP 2018 universal questions Preliminary Round
The first 17 questions
From 1 to 2018 in which the number of 2018, a total number __________ contain numbers 8.
This question should be done using a combination of knowledge count, the first consideration is the complement to 1 in 2018 does not include the number of 8 digital numbers.
1 digit, a total of eight.
2 bits, because each one can have a first 8 and is not 0, it is \ (9 * 8 = 72 \) a,
3 digits Similarly, \ (8 * 9 * 9 = 648 \) a.
Is divided into 4 bits 1000 to 1999 and 2000 to 2018 considering two parts, 1000 to 1999, in \ (1 * 9 * 9 * 9 = 729 \) a, in 2000-2018 with a \ (2018-2000 + 1- 2 = 17 \) a.
Therefore, a total of \ (2018-1 1-8-72-648-729-17 = 544 + \) a digital number comprising 8