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. How many books are there in children's stories?
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. A highway with a length of 172km was built for 4 days, with an average of 18m per day. The rest is required to be completed in 5 days, how many kilometers per day on average?
6. The names of A, B, C and D are very interesting: A is B, B is C, C is D, and D is A.. It is also known that the names of the four people are only Liu, Bai, Ding and Yang, and no one is named, while the surname D is another person's surname, and the first name of the surname is Liu.
7. A cuboid is 9 decimeters long. If you cut it into two cuboids along its height, the surface area will increase by 4 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 the 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. 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?
It can be known 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 "the number of people who won the gold medal is less than the number of people who won the silver medal" to the total number, so a * * * has six-fifths =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. How many books are there in children's stories?
One-half of children's cartoons MINUS one-sixth equals one-third, and the juvenile stories remain unchanged, but their total number is 24-20=4, so one-third of children's cartoons = 12, and half is 6, so one-quarter of juvenile stories are 24-6= 18, so
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?
When the drum rolls once, the forward distance is the circumference of the drum bottom, that is, L=πD(D is the diameter) = 0.8 π, 10 turns forward 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?
It can be known 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 the 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. A highway with a length of 172km was built for 4 days, with an average of 18m per day. The rest is required to be completed in 5 days, how many kilometers per day on average?
It was repaired for 4 days, with an average of 18m per day, so it was repaired for 4 *18 = 72m,172-72m =100m. It will take five days to finish the repair, so the average daily cost is 100÷5 = 20 meters.
6. The names of A, B, C and D are very interesting: A is B, B is C, C is D, and D is A.. It is also known that the names of the four people are only Liu, Bai, Ding and Yang, and no one is named, while the surname D is another person's surname, and the first name of the surname is Liu.
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 you cut it into two cuboids along its height, the surface area will increase by 4 decimeters. Do you know the volume of the original cube?
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 the father and son?
Assuming that 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+32.