1. If the difference between two four digits is equal to 892 1, it is said that these two four digits form a number pair. How many pairs of such numbers are there?
Analysis: Consider this problem from two extremes: 9999- 1078=892 1, and the minimum value is 9921000 = 8921,so * * has 999-992655.
2. A book starts with 1 page, and * * * uses 2355 numbers, so how many pages does this book * * * have?
Analysis: classified by digits: one digit: 1 ~ 9 * * * Banded digits1* 9 = 9; Two digits: 10 ~ 99 * * * Use the number 2 * 90 =180;
Three digits: 100 ~ 999 * * * Use the number 3*900=2700, so the number of pages required should not exceed 999. The three digits * * * are: 2355-9- 180=2 166, 2 166 respectively.
3. The page numbers of the first and second volumes are 687, and the first volume is 5 pages more than the second volume. How many pages are there in the first volume?
Analysis: One digit has 9 digits, and two digits have 180 digits, so both upper and lower digits pass through three digits. The sum difference problem is used to solve problems: the sum is 687, the difference is 3*5= 15, and the large number is: (687+ 15) ÷ 2 = 3565433.
4. From the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, how many different products can be obtained by multiplying the sum of five numbers with the sum of the other five numbers?
Analysis: The whole group is divided into two groups and the sum remains unchanged:1+2+3+4+5+6+7+8+9+10 = 55. From the extreme point of view, the two groups that are divided into minimum sums are (1+2+3+4+5)+(6+7+).
Another number from 15 to 27 can be combined.
5. Write down all the natural numbers of 1 and get:1234567891kloc-0/11213 ...
Analysis: Similar to the previous question, the same knowledge point: one digit is 9 digits, two digits 180 digits, three digits are 2700 digits, and four digits are 36000 digits, leaving: 206788-9-180-2700-36000 =1.
6. How many different ways are there to make 1 yuan with 0, 2 and 5 cents?
Analysis: classification and addition: there are only three combinations of a coin; Combination of 1 and 2 points: 2 points can range from 1 to 49 blocks, and there are 49 methods; Combination of 1 and 5 points: the number of 5 points can range from 1 to 19, and there are 19 methods; Combination of 2 points and 5 points: There are 9 methods for 5 points: 2, 4, 6, ..., 18 * * *; Combination of 1, 2,5 points: because 5= 1+2*2, 10=2*5,15 =1+2 * 7,20 = 2 */kloc-0.
7. In the picture, starting with the word "Hua", whenever you move down to an adjacent word, you can read "Hua Pai". So how many different pronunciations of * * *?