Analysis of the Olympic Mathematics Test Questions and Answers in the Fourth Grade of Primary School (1)
The grass on the grassland grows at a uniform speed. If 20 sheep can eat all the grass and new grass in 5 days, it will take 14 sheep 10 days to finish. So if you want to eat all the grass on this grassland in four days, you need _ _ sheep. A, 22
B, 23
c、24
Analysis:
Suppose 1 sheep eats one day 1 grass. The amount of new grass per day is: (14×10-20× 5) ÷ (10-5) = 8 (copies). The amount of grass is: 20×5-8×5=60 (parts). Eight sheep are specially arranged to eat new grass every day.
Analysis of the Olympic Mathematics Test Questions and Answers in the Fourth Grade of Primary School (Part Two)
30 cars and 3 trucks carry 75 tons at a time, and 45 cars and 6 trucks carry 120 tons at a time. How many tons does each truck and car transport at a time? Answer and analysis:
Excerpt condition: 30 cars +3 trucks =75 tons.
45 cars +6 trucks = 120 tons
Compared with the conditions, it is converted into: 60 cars +6 trucks = 150 tons.
45 cars +6 trucks = 120 tons
It can be seen from the change of the corresponding quantity that (150- 120) tons just corresponds to the load capacity of (60-45) cars, so each car can transport 2 tons at a time, and each truck can transport 5 tons at a time.
Analysis of the Olympic Mathematics Test Questions and Answers in the Fourth Grade of Primary School (3)
7 bags of rice, weighing 12kg, 15kg, 17kg, 20kg, 22kg, 24kg and 26kg respectively. A buys a bag first, and the rest is bought by B, C and D. It is known that the weight bought by B and C is exactly the same, twice that of D. Ask the weight of the bag of rice bought by A first. analyse
Because b and c buy as much weight as d and both weigh twice as much as d.
So the weight bought by three people is five times that of Ding;
The total weight of seven bags of rice is12+15+17+20+22+24+26 =136 kg.
136 kg minus a multiple of 5, the rest is the weight bought by A..
Conversely, if you subtract the weight of the bag of rice bought by A from 136 kg, the remaining weight must be a multiple of 5. In order for the sum of 136 to be divisible by 5, the unit number of this number must be 1 or 6, and only 26 out of 7 bags of rice are 6;
So, the weight of the bag of rice bought by A is 26 kilograms.
Analysis of the fourth grade Olympic math test questions and answers in primary school
Xiaoming has two roads with the same length from home to school, one is a flat road and the other is a half slope. Xiao Ming takes as much time to go to school by two roads. It is known that the downhill speed is 1.5 times that of the flat road, so how many times is the uphill speed? Up and down the slope to answer:
If the distance is 180, then both uphill and downhill are 90. Let the level speed be 2, then the downhill speed is 3. Downhill needs 90/3=30, straight road needs 180/2=90, so uphill needs 90-30=60. It takes 90/2=45 to walk the same distance as uphill. Because speed is inversely proportional to time, the uphill speed is 45/60=0.75 times of the downhill speed.
Analysis of the Test Questions and Answers of Olympiad Mathematics in the Fourth Grade of Primary School (5)
Daqiang and Xiao Qiang * * * have 100 apples. There are four more apples in Daqiang than in Xiao Qiang. How many apples are there in Daqiang and Xiao Qiang? Answer and analysis:
After removing four strong apples, the number of strong apples is twice that of Xiao Qiang, and the total number of apples at this time is equivalent to three times that of Yu Xiaoqiang.
So there are apples in Xiao Qiang (100-4)÷3=32 (pieces),
So Daqiang has apples 100-32=68 (pieces).
Analysis of Olympiad Mathematics Test Questions and Answers in the Fourth Grade of Primary School (VI)
The geography teacher hung a map of the world on the blackboard and marked the five continents with code names, so that the students could recognize them. The five students answered as follows: No.3 is Europe, No.2 is America;
B: No.4 Asia, No.2 Oceania;
C: 1 number is Asia, and number 5 is Africa;
D: No.4 is Africa and No.3 is Oceania;
E: Europe on the 2nd and America on the 5th.
The teacher said that each of them was only half right. No.65438+0 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Answer and analysis: 1 is Asia; No.2 is Oceania; The third place is Europe; The fourth place is Africa; The fifth is the United States.
Answer the question: If the first half of A is correct and No.3 is Europe, it is wrong to infer that No.3 is Oceania. Since everyone is only half right, it can be seen that Ding is right to say that No.4 is Africa, and thus B is wrong to say that No.4 is Asia and No.2 is Oceania. It is also known that E is wrong to say that No.2 is Europe and No.5 is America, which leads C to say that No.5 is Africa and 1 is Asia. Finally, the correct conclusion is: No.65438 +0 is Asia; No.2 is Oceania; The third place is Europe; The fourth place is Africa; The fifth is the United States.