1 digit, 9 pages in total.
The 2-digit page number is 10-99, and * * uses 90*2= 180.
The 3-digit page number is 100-683, and * * is 584*3= 1752.
Then * * * use 9+180+1752 =1941digit.
(2) 1-99, occurrence times1=10+10 = 20 times. (The first 10 refers to the decimal number 1 multiplied by 10- 19).
The frequency of 100- 199, 1 = 100+20= 120. (100 means the hundredth number of 100- 199).
200-599, frequency of occurrence 1 =5*20= 100 times.
600-683, frequency of occurrence 1 = 10+9= 19.
Then the total number of occurrences of 1 is 20+120+100+19 = 259.
1、
It takes 4889 numbers to rank the page numbers of a dictionary. This dictionary has 750 pages (printed on both sides).
Suppose this dictionary * * * has x pages, because the number of pages to 999 is 9+ 180+2700 = 2889, so x is at least greater than 1000 pages.
Column equation:
2889+(X- 1000+ 1)* 4 = 4889
X-999=2000/4=500
X= 1499 .
Double-sided printing, page number = 1499/2=750.
2. All four digits less than 1993 are arranged in descending order, and the middle four digits are 1496.
Basically, it is the same as the number in the middle of 0- 12 and can be counted.
3、
66660。 (use? 1、2、? Three, four, four numbers make up a non-repetitive four-digit * * *? 4*3*2=24. Every number? Six? 1, 2, 3 and 4 add up, right? 60)
The premise of this question is that the bus starts to pick up and drop off on time every day. Then the time it takes this person to walk a certain distance is the time saved by the car going back and forth, that is, 10 minute. Then the distance is 50 *1/6 *1/2 = 25/6 km.
According to the meaning of the question, this person walks 50 minutes away = 5 minutes away from the enterprise. Then this person's speed is110 of the enterprise, which is 50 *110 = 5 km/hour.
6. Drawing description of this topic. Set the bus speed v and departure interval t, as shown in the figure:
At a certain moment, 1 caught up with Xiao Ming at point A and met Xiao Ming. The second car, car No.2, is at point C. After 9 minutes, Xiaoming walks to point B. Car No.2 catches up with Xiaoming.
The bus travels for 9 minutes, the AC distance is vt, the AB distance is 4*9/60, and the BC distance is v*9/60. Equation according to the meaning of the question:
v*9/60=vt+4*9/60
Similarly, according to the time when the opposite bus arrives in Xiaoming in 6 minutes, make the equation:
vt=(v+4)*6/60
The solution is v = 20km/h and t = 7.2 minutes. ..