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General solution: A total of 789 numbers are needed to compile the pages of this book, and it is estimated that the total number of pages of the book should not exceed three digits. Since it is no more than three digits, it can be calculated by classification.

There are 9 pages with only one digit code, and 9 digits are shared; There are 90 pages (from page 10 to page 99) that need to be coded with two numbers, sharing (2 90) 180 numbers; The next two are encoded with three numbers, leaving (789 9 180) 600 numbers, and (600 3) 200 pages, that is, the book has 299 pages. The composite formula is: 9 + 90 + 789 1 9 2 (99 9) 3 = 299 (page).

Clever solution: Since the total number of pages in this book does not exceed three digits, we may wish to assume that each page of the book uses three numbers, that is, we should add two "0s" before the page number of 1 9 pages, adding a total of (2 9) 18 "0s"; Add a "0" before each page number on page 10 99 for a total of (1 90) 90 "0s". In this way, there are (789 + 18 + 90) 897 numbers, and each page uses 3 numbers, which can be compiled into (897 3) 299 pages, that is, the book has 299 pages.

The composite equation is: 789+2 9+1 (99 9) 3=299 (page).

Because 9*1+90*2+200*3=789. So, the book has 199 pages.

Because, 1-9 are all one-digit numbers, 10-99 are two-digit numbers, and the rest is a three-digit problem, exactly 200, but the first three-digit number is 100 instead of 101, so there is the answer.

1 9 9 pcs.

10 99 90 * 2 = 180.

100 299 200 * 3 = 600.

So: the book has 299 pages.

There are 9 for one number, 90 for two digits, and 900 for three digits.

So the number of pages is in three digits.

So the number of pages is the 200th three-digit number, which is 299

The book has 299 pages.

Let's start with the single-digit page number, which is 9 digits. Look at the two-digit page number again, and use 2 90 = 180 numbers. Now you estimate that because there are 900 three-digit numbers, the number of pages in this book is three-digit.

Use 789-9-180 = 600 digits, indicating that 600 digits are used in three digits, and since each three-digit number has three digits, 600 3 = 200 digits are used, indicating that 200 digits are used in three-digit numbers, and the last digit is the last digit of the 200th three-digit number. Using 100+200-1=299 pages, we can find out what the second hundredth three-digit number is, which is the number of pages in the book.

This method is called the step-by-step calculation method, which is the "addition principle" in the Olympiad.

Is 10 counted as 2 numbers? Then 100 is considered 3?

I think the two numbers are 4 and 6

For B, if he were told that the sum was 5, he would obviously be able to guess immediately that it was 2 and 3, because the two smallest numbers without 1 are 2 and 3And the greater the sum, the more likely it is to form this sum, so it is more difficult to guess; For c, since there is no 1, the product of the two numbers must be composite, so all prime numbers, i.e., prime numbers, can be excluded. If the product is a composite number made up of two prime numbers, e.g. 4, 6, 10, ,......Then c will immediately guess the result, but now it is not guessed, so these numbers can be excluded, of course, 8, 16, 27 should also be excluded, and the remaining numbers are 12, 18, 20, 24, 28, 30, 32, 36, 40, 42, 44, 45, 48, etc.

When C says that he didn't guess it, B says that he guessed the result, because only one of the two numbers that make up the sum satisfies the condition, such as the sum is 7, it can't be 2 and 5, there are only 3 and 4, and the product is 12, but if the product is 12, C still can't guess the result, because the conditions are 2 and 6 and 3 and 4, because the sum of 2 and 6 is 8, and the sum that satisfies and is 8 cannot be 3 and 5, nor can it be 4 and 4, only 2 and 6, that is, the condition is also unique, so C cannot be determined, so the condition is not satisfied, and the condition is not satisfied, so the result is 24, these two numbers are 4 and 6 respectively, the sum is 10, there are 2 and and 5 and the three groups of numbers are not satisfied, only 4 and 6, and its product is 24.

There are 4 chickens and 4 ducks in the first picture, which are sold for a total of 228 yuan, so a chicken and a duck are sold for 228 4 = 57 yuan; In the second picture, there are 3 chickens and 2 ducks selling for a total of 139 yuan, then, a chicken sells for 139-57 2=25 yuan; A duck sells for 57-25 = 32 yuan.

The two places are 140x meters apart, according to the title.

80(160x/60-14)=120x,2(8x/3-14)=3x,16x/3-28=3x,7x/3=28,x=12,140x=1680.

1. The dividing tens of digits are 0, because the divisor has dropped two places in a row; 2. The unit digit of the divisor is 4, because the unit of the dividend is 7 and the remainder is 1, it can be seen that the unit of the divisor and the product of the quotient 9 is 6, and only 4 9 = 36. Thus the divisor is 64; 3. The hundredth place of the quotient is 1, because only 1 64 can get the product of two digits. So the dividend is 109 64 + 1 = 6977.