Analysis: This question does not require area. It is only necessary that the length and width are several times the diameter of the circle, and then the product of the multiples of the length and width is found.
1 m 20cm =120cm
120÷30=4
90÷30=3
4×3= 12 (block)
A: You can cut 12 pieces at most.
2. A cylinder with a bottom radius of 1 decimeter has a square profile. What is the surface area and volume of this cylinder?
Analysis: Starting from the square of the side expansion diagram, we can know that the height of this cylinder is the circumference of the bottom of the cylinder.
Surface area of cylinder:
(3. 14× 1×2)×(3. 14× 1×2)+3. 14× 1× 1×2
=6.28×6.28+6.28
=6.28×7.28
=45.7 184 (square decimeter)
Cylinder volume:
3. 14× 1× 1×(3. 14× 1×2)
=3. 14×6.28
= 19.7438+092 (square decimeter)
A: The surface area of this cylinder is 45.75438+084 square decimeter, and the volume is 19.438+092 square decimeter.
A train leaves from Station A at 8 a.m. and arrives in bilibili at 9 p.m. the next day. As we all know, the train travels at an average speed of 98 kilometers per hour. How long is the railway between Station A and bilibili?
Analysis: The key to solve this problem is to know the time of the train.
24-8+9=25 (hours) [or: 12-8+ 12+9=25 (hours)]
98×25=( 100-2)×25
=2500-50
=2450 km
A: The railway between Station A and bilibili is 2450 kilometers long.
The circle and the sector have the same radius. It is known that the area of a circle is 30 square centimeters and the central angle of a sector is 72 degrees. Find the area of the sector.
Analysis: Because the radii of a circle and a sector are equal, the area of a circle and a sector should be multiple. This multiple is the multiple relationship between their central angles.
72÷360= 1/5, 30× 1/5=6 (square centimeter)
The area of this sector is 6 square centimeters.
Question 1 1: Draw a sector in a circle with a radius of 3 cm so that its area accounts for 20% of the area of the circle, and calculate the area of this sector.
Analysis: This question is the same as the above question.
3. 14×3×3×20%=5.652 (square centimeter)
A: The area of this area is 5.652 square centimeters.
5. The school divided the task of planting trees into 6 levels and 5 levels according to 5: 3. The sixth grade actually planted 108 trees, exceeding the original task by 20%. How many trees were planned to be planted in the fifth grade?
Analysis: The number of trees planned for the sixth grade is the key to solve the problem.
/kloc-How many trees were originally planned to be planted at Grade 0 and Grade 6?
108 ÷ (1+20%) =108× 5/6 = 90 (tree)
2. How many trees were planned to be planted in the fifth grade?
90÷5×3=54 (tree)
Comprehensive formula:
108÷( 1+20%)÷5×3
=90÷5×3
=54 (tree)
A: It was originally planned to plant 54 trees in the fifth grade.
6. Two engineering teams, A and B, completed a section of the road, and the working efficiency of Team A was three-fifths that of Team B. Two teams completed two-thirds of the road in six days, and the rest was repaired by Team B alone. How many days will it take to finish it?
Analysis: Finding the working efficiency of two teams is the key to solving the problem.
1. What is the sum of the work efficiency of the two teams?
2/3÷6= 1/9
2. How efficient is Team B?
1/9×[5÷(3+5)]
= 1/9×5/8
=5/72
3. How many days will it take to complete?
( 1-2/3)÷5/72
= 1/3×72/5
=24/5 (days)
A: It will take another 24/5 days to complete.
7. A cement factory produced 232,400 tons of cement last year. The output in the first five months of this year is equal to that in the whole of last year. According to this calculation, the output of this cement plant will increase by a few percent this year compared with last year.
Scheme 1: The analysis shows that the output will increase in the last seven months of this year, so we have to calculate the output in the last seven months first.
232400÷5×( 12-5)
=46480×7
=325360 (ton)
325360÷232400= 1、4= 140%
Scheme 2: "1" with the unit of 232,400 tons,
1. Compared with last year, what is the average monthly output this year?
1÷5= 1/5
2. How much has the output increased this year compared with last year?
1/5×( 12-5)=7/5
Compared with last year, what percentage has the output increased this year?
7/5= 1.4= 140%
Comprehensive formula:1÷ 5× (12-5) =1.4 =140%.
The output of this factory this year has increased by 140% compared with last year.
8. The kindergarten bought 40 towels of different sizes, which cost 258.8 yuan. The unit price of a large towel is twice that of a small towel, with a difference of 0. 1 1 yuan. What is the unit price of these two kinds of towels?
Solution: If the unit price of a small towel is X yuan, then the unit price of a large towel is (2x+0. 1 1) yuan.
[x+(2x+0. 1 1)]×40 = 258.8
3x=6.47-0. 1 1
x = 6.36 \3
x=2. 12
2x+0. 1 1 = 2. 12×2+0. 1 1
=4.35
A: The unit price of large towels is 4.35 yuan each, and the unit price of small towels is 2. 12 yuan each.
9.
A room with a length of 4-8m and a width of 3-6m needs 768 square bricks with a side length of 0,15m. A room 6 meters long and 4 or 8 meters wide, how many tiles do you need if you use the same tiles? How many square bricks with a side length of 0 or 2 meters should be used in the first room? (Use proportional solution)
Analysis: The area of the room is fixed, and the area of each brick is inversely proportional to the number of blocks.
Solution: Suppose X blocks are needed.
0. 15×0. 15x
=6×4.8
x
=6×4.8÷0. 15÷0. 15
x
= 1280
A: Yes 1280 yuan.
Solution: suppose you need y blocks.
0.2×0.2y=4.8×3.6
y=4.8×3.6÷0.2÷0.2
y=432
A: It's 432 yuan.
10. Shipborne diesel can be used for up to 6 hours. When driving out, it was downwind, with a speed of 30 kilometers per hour. When driving back against the wind, the distance per hour is 4/5 of that when driving with the wind. How far should the ship sail before returning?
Analysis: The distance traveled by a ship is constant, and the distance traveled per hour is inversely proportional to time.
Solution: Suppose the ship sailed against the wind for x hours.
30×4/5x=30×(6-x)
4/5 times =6 times
9/5x=6
x= 10/3
30× 4/5×10/3 = 80km.
A: This ship should sail for 80 kilometers at most.
1 1.
Car A traveled17 in the first hour and 16 km more in the second hour from place A to place B.. At this time, it is 94 kilometers away from B. How many kilometers is the expressway between A and B?
Analysis: "The second hour is longer than the first hour 16km", which means that the second hour is 1/7, 16km. The first hour and the second hour * * * are (1/7+ 1/7) and 16 km respectively. It can be seen that (96+ 16) accounts for the whole process (1- 1/7- 1/7).
According to the above analysis:
(96+ 16)÷( 1- 1/7- 1/7)
= 1 12÷5/7
= 1 12×7/5
=156.8km.
A: The length of the highway between A and B is156,8km.
Or solve by equation:
Solution: Suppose the expressway between A and B is x kilometers long.
( 1- 1/7- 1/7)x = 96+ 16
5/7x= 1 12
x= 156、8
A: The length of the highway between A and B is156,8km.
Topic adaptation: If one of the conditions in this question is changed to "96 kilometers away from a certain place at this time", other conditions will remain unchanged and the problem will remain unchanged. How to answer?
12. A knitting group originally produced 1500 flower baskets for 30 people 10 day. Now it has increased to 80 people. According to the original work efficiency, how many days does it take to produce 6000 flower baskets? (Answer in proportion)
Analysis: the title says "according to the original working efficiency", which shows that the working efficiency of this textile group is certain. The work efficiency is certain, and the total amount of work is directly proportional to the working hours.
Solution: Suppose it takes X days.
1500:(30×50)=6000:(80×x)
1500×(80×x)=6000×(30×50)
x=6000×30×50÷80÷ 1500
x = 6000÷ 80
x=75
A: It takes 75 days.
13. There are two wheat fields in Hong Guang Farm, the first is 5.5 hectares, the second is 3.6 hectares, and the second is 18.2 tons. How many tons of wheat are harvested on average per hectare in these two wheat fields?
14.
It took the bus three hours to climb the mountain, averaging 30 kilometers per hour. It takes only two hours to go down the mountain on the same journey. Find the average speed of the car going up and down the mountain.
15.
Party A and Party B walk in opposite directions from the same place at the same time. Party A travels every hour15km, and Party B travels every hour12km. How many kilometers are they apart in 4.5 hours? How many kilometers did A walk more than B?
16.
Clothing factory plans to make 1470 sets of clothing, which has been done for five days, with an average of 150 sets per day. The remaining 4.5 days are completed, and how many sets are made on average every day?
17.
Each set of children's clothing cloth is 2.5m, and each set of adult clothing cloth is 4m. Now we have to make 5 sets of children's clothes and 3 sets of adult clothes, and there are 30 meters of cloth. How much rice cloth can we leave? If each pair of trousers is made of cloth 1. 1 m, how many pairs of trousers can be made of the remaining cloth?
18. The supermarket launched the activity of "buy 5 get free 1" for mineral water. There are 48 people in a tour group. How many bottles of water do you need to buy if you want to give everyone a bottle of mineral water?
(buy 5 get free 1)
You only need to buy five bottles of six bottles of mineral water, and 48 has eight sixes, so you only need eight fives. The answer is 40 bottles. )
19.
The decimal part is two decimal places. Rounded to the nearest 0. 1, the approximate value is 5.0. So what is the decimal of this two-digit number?
(Analysis: The required two decimal places are: 4.95, 4.96, 4.97, 4.98, 4.99, 5.00, 5.0 1, 5.02, 5.03 and 5.04.
20.
A cuboid iron box has a square bottom. If one side of it is unfolded, a square with a side length of 40cm is obtained. What is the volume of this iron box?
《
40÷4= 10
10× 10×40÷ 1000=4》
Respondents:
cyg2436
-
higher level manager
Seven grades
1- 12
15: 16
Topic selection of Olympic mathematics in the fifth grade of primary school
fill-in-the-blank question
1. Calculation: 0.02+0.04+0.06+0.08+…+19.94+19.96+19.98 = _ _ _ _ _.
2./kloc-0 /×1+2× 2+3× 3+...1997×1998×1998 is _ _ _ _ _
3. A two-digit number, add a 0 between its two digits, which is 630 more than the original number. Such two digits are _ _ _ _ _.
At present, there are four RMB 1, two RMB 2 and three RMB 10. If you take at least 1 piece and at most 9 pieces, then * * * can be made into _ _ _ _ _ _.
5. A set of four digits, each digit is not 0 and different from each other, but the sum of all digits of each digit is 12. Put these four numbers in descending order, and the 25th place is _ _ _ _ _ _ _ _.
6. The big monkey gives the little monkey peaches. If each monkey gets 8 peaches, there are 10 peaches left. If each little monkey is divided into 9 peaches, then a little monkey will be divided into less than 9 peaches, but it can still be divided into peaches, small ones.
8. There is a residential building, and each family subscribes to two different newspapers. This residential building subscribes to three newspapers. Among them, there are 34 Nantong radio and television newspapers, 30 Yangzi Evening News and 22 newspaper abstracts. Then, Yangzi Evening News and Newspaper Digest have _ _ _ _ _ _ subscribers.
9. Qiang Qiang and Fang Fang run back and forth in a straight line, with a distance of 120 meters. Qiang Qiang runs 2 meters per second and Fang Fang runs 3 meters per second. If two people start from both ends at the same time, then * * * meets _ _ _ _ times in 15 minutes.
10. A workshop has processed a batch of parts and plans to process 48 parts a day. Actually, 12 pieces were processed more than planned every day, and the task was completed 5 days ahead of schedule. This batch of parts * * * has _ _ _ _.
(Adapted from the 427 issue of "Decimal Newspaper")
1 1. The sum of the ages of Li, Sun and Wang this year is 1 13 years old. When Wang was 38 years old, Sun was twice as old as Li. When Li 17 years old, Wang was twice as old as Sun. Sun is _ _ _ _ _ _ _ _ years old this year.
(Decimal newspaper 492,98-9-18)
(Decimal Report 475)
13. There are 16 locks and 20 keys, of which 16 and 16 of 20 keys are paired one by one, but now the locks and keys are confused. Then, you need to try at least _ _ _ _ times to make sure that the lock and key match.
(Decimal newspaper 457, adapted)
(adapted from decimal newspaper 475,98-4 98-4- 10/0)
15. Four students, A, B, C and D, participated in the math competition for primary school students in Nantong. Before the competition, three teachers made predictions:
A teacher said: C first, A second;
Another teacher said: B is the first and D is the fourth;
There is also a teacher: Ding comes second and C comes third.
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