Use tabular method, as shown in the following table.
14. Three students A, B and C bought 24 buttons with different quantities. Take out the same number of buttons as B from A for the first time and merge them into B; The second time, take out the same number of buttons as C from B and merge them into C; The third time, I took out as many buttons as A from C and merged them into A ... After this change, the number of buttons of three people is exactly the same. It is known that student C originally spent 0.3 yuan on buttons. How much did students A and B spend on buttons?
A: A originally spent 0.55 yuan (55 cents) on buttons, and B originally spent 0.35 yuan (35 cents) on buttons.
Find the number of buttons per person after the change. 24? 3=8 (pieces). Then, the backward deduction method combined with the list method is used for analysis, as shown in the following table.
0.3 yuan =30 points, 30? 6=5 (points)
How much did it cost to buy buttons? 5? 7=35 (minutes) (that is, 0.35 yuan)
How much did it cost to buy buttons? 5? 1 1=55 (minutes) (that is, 0.55 yuan)
15. There are three piles of matches on the table. Xiao Cong moved them according to the following two principles: ① Take some from the first pile and put them in the second pile; Take a few from the second pile and put them in the third pile; Take some from the third pile and put them in the first pile. (2) Take four more matches than the original pile of matches. With such a walk, each pile of matches is exactly 12. How many matches are there in each pile?
A: The first pile 18 matches, the second pile 10 matches, and the third pile 8 matches.
The backward method is adopted, starting from each pile 12. According to the meaning of the question, the last 12 root of the first pile is obtained by adding the same number of roots and adding 4 to all the previous roots, so the number of the previous roots is (12-4)? 2=4 (root). Finally, the third heap should be added to the first heap, which should be 12+4+4=20 (root). The following can be expressed in tabular form by analogy (as shown in the following table).
16. There is a square pool with an outer edge of 40 meters. Surround a circle of iron railings along the outer edge, bury a vertical iron pipe at each corner, and bury another vertical iron pipe every 2 meters. How many vertical iron pipes can be buried? (Please answer in different ways)
A: Four dollars and eighty cents.
Solution 1: 40? 4? 2= 160? 2=80 (root)
Option 2: (40? 2+ 1)? 2+(40? 2- 1)? 2
=2 1? 2+ 19? 2=42+38=80 (root)
Option 3: (40? 2? 2+ 1)+(40? 2? 2- 1)
=4 1+39=80 (root)
17. There is a locust tree every 7 meters on both sides of the road. Xiaojun took a trolley bus for 3 minutes and saw a locust tree on the side of 15 1. How many kilometers does the trolley bus travel per hour? (1 km =1000m)
Answer: 2 1 km.
First calculate the distance traveled by trolleybus for 3 minutes, then calculate the distance traveled per minute, and finally calculate the distance traveled per hour.
7? ( 15 1- 1)? 3? 60? 1000
=7? 150? 3? 60? 1000
=2 1 (km)
or
7? ( 15 1- 1)? (60? 3)? 1000
=7? 150? 20? 1000
=2 1 (km)
18. To celebrate the 40th anniversary of the founding of People's Republic of China (PRC), a parade of 52 floats was reviewed, each with a length of 4m, a distance of 6m between the front and rear cars, and the speed of the motorcade was105m per minute. How many points does this train team need to pass through the 536-meter-long parade ground?
Answer: 10.
The distance traveled by the motorcade is equal to the sum of the length of the inspection site and the length of the motorcade.
[4? 52+6? (52- 1)+536]? 105
=(208+306+536)? 105
= 1050? 105
= 10 (minimum)
19. Xiao Zhi's father's salary is twice that of his mother. His father took out 180 yuan from his salary and bought a bicycle, which is exactly half of Xiao Zhi's parents' total salary. How much is Xiao Zhi's father's monthly salary?
A: 240 yuan.
Because 180 yuan is just half of Xiao Zhi's parents' total salary, his parents' total salary is 180? 2=360 yuan. Xiao Zhi's father's monthly salary is:
180? 2? (2+ 1)? 2= 120? 2=240 (yuan)
20. The number of kilograms of white sugar divided by the number of kilograms of brown sugar in the grocery store is exactly 3, and the number of kilograms of white sugar plus the number of kilograms of brown sugar plus the quotient is 163. How many kilograms are there in white sugar and brown sugar?
Answer: 4. 40kg of brown sugar and 0/20kg of white sugar/kloc.
According to? The kilograms of white sugar divided by the kilograms of brown sugar is exactly 3? The weight of white sugar is three times that of brown sugar. What is the basis? Kg of white sugar plus kg of brown sugar 163? The sum of the weights of white sugar and brown sugar is 163-3.
( 163-3)? (3+ 1)=40 (kg) (brown sugar)
40? 3= 120 (kg) (sugar)