2. Among the extracurricular reading materials in the school library, it is known that one-half of children's cartoons and one-quarter of teenagers' stories are 24; One sixth of children's cartoons and one quarter of children's stories are twenty books. How many juvenile stories are there?
3. A roller with a drum length of10m and a diameter of 0.8m.. If the drum rolls 10 times, how many meters will it advance? How many square meters of pavement does it cover?
4. Cut the largest semicircle on a rectangular piece of paper with a length of 30cm and a width of 20cm. How many square centimeters is the remaining area?
5. Building a highway with a length of 172km has been completed for 4 days, with an average of 18m per day. The rest are required to be repaired within 5 days. How many kilometers are repaired on average every day?
6. The names A, B, C and D are very interesting: A is the surname B, B is the surname C, C is the surname D, and D is the surname A.. I also know that the names of the four people are only Liu, Bai, Ding and Yang. No one is. Dante's name is another person's surname, and this person's name is Liu's surname. Please write down the names of these four people.
7. A cuboid is 9 decimeters long. If it is cut into two cuboids along its height direction, the surface area will increase by 4 square decimeters. Do you know the volume of the original cube?
8. There is a father and son. When asked about their age, my father replied, "Before 16, I was three times as old as my son, and now I am twice as old as him." How old are father and son?
Answer:
1. In an Olympic Games, the number of people who won gold medals accounted for one-fifth of the number of people who won medals, and the number of people who won silver medals accounted for two-sevenths of the number of people who won medals. It is understood that the number of people who won the gold medal is 6 less than that who won the silver medal. How many people won medals?
Solution: We can know that the number of people who won the gold medal is less than the number of people who won the silver medal "two-sevenths minus one-fifth" = three-fifths, that is, the ratio of "six people who won the gold medal are less than six people who won the silver medal" to the total number, so one * * * has six 35 =70 people.
2. Among the extracurricular reading materials in the school library, it is known that one-half of children's cartoons and one-quarter of teenagers' stories are 24; One sixth of children's cartoons and one quarter of children's stories are twenty books. How many juvenile stories are there?
Solution: One-half of children's cartoons minus one-sixth equals one-third, and juvenile stories remain unchanged, but their total number is 24-20=4, so children's cartoons have 4- one-third = 12, and half is 6, so a quarter of juvenile stories is 24-6= 18.
3. A roller with a drum length of10m and a diameter of 0.8m.. If the drum rolls 10 times, how many meters will it advance? How many square meters of pavement does it cover?
Solution: When the drum rolls once, the forward distance is the circumference of the drum bottom, that is, L=πD(D is the diameter) =0.8π, 10 before turning 10*0.8π=8π.
The compression area is S=8π* 10=80π.
4. Cut the largest semicircle on a rectangular piece of paper with a length of 30cm and a width of 20cm. How many square centimeters is the remaining area?
Solution: We can know that the largest semicircle is a semicircle with a long side diameter of 30cm and a radius of 15cm, which is just within the scope of this paper. So the area of the semicircle =0.5πr? = 0.5π *15 *15 =12.5π, so the remaining area = 20 * 30-12.5π = 600-/kloc-. )
5. Building a highway with a length of 172km has been completed for 4 days, with an average of 18m per day. The rest are required to be repaired within 5 days. How many kilometers are repaired on average every day?
Solution: It was repaired for 4 days, with an average of 18 meters per day, so it was repaired for 4 * 18 = 72 meters, and 172-72 = 100 meters. It takes 5 days to complete the repair, so it takes an average of 65,438+000 ÷ 5 = days per day.
6. The names A, B, C and D are very interesting: A is the surname B, B is the surname C, C is the surname D, and D is the surname A.. I also know that the names of the four people are only Liu, Bai, Ding and Yang. No one is. Dante's name is another person's surname, and this person's name is Liu's surname. Please write down the names of these four people.
Solution: Poplar, willow, Liu Ding, Dingbai; Ding Bai, Poplar, Willow, Liu Ding; Liu Ding, Ding Bai, Yangliu; Willow, Liu Ding, Dingbai, Poplar.
7. A cuboid is 9 decimeters long. If it is cut into two cuboids along its height direction, the surface area will increase by 4 square decimeters. Do you know the volume of the original cube?
Solution: The increased surface area is the original side *2, which is exactly the volume of the original cube multiplied by the side length, so V=4*9÷2= 18 square decimeter.
8. There is a father and son. When asked about their age, my father replied, "Before 16, I was three times as old as my son, and now I am twice as old as him." How old are father and son?
Solution: If the son was X years old before 16 and the father was 3x years old before 16, now the son is x+ 16 and the father is 3x+ 16, which is twice as much as the former, that is, 3x+16 = 2x+36.