# Examples for 8th grade - page 102 Lucy, Tereza, and Petra decided to compile the compulsory reading records together. It would take 30 days for Lucia alone, 36 for Tereza and 45 for Petra. How long will take make records if they will work together?
2. Body diagonal Calculate the cube volume, whose body diagonal size is 75 dm. Draw a picture and highlight the body diagonal.
3. Slant height The slant height of cone is 5cm and the radius of its base is 3cm, find the volume of the cone
4. Mushrooms Fresh mushrooms contain 88% water, dried 14% water. How many kilograms of fresh mushrooms should be collected to get 3 kg of dried?
5. Two buses The first bus runs 15 minutes the second bus runs after 21 minutes. Together they both leave at 7:00 on Monday. When and what day will they meet?
6. Rhombus 29 One of the diagonals of a rhombus is equal to a side of the rhombus. Find the angles of the rhombus.
7. Bulbs There are 875 identical light bulbs in the sports hall lightning for 2 hours. How long does it lightning 100 this light bulbs?
8. Sum of squares The sum of squares above the sides of the rectangular triangle is 900 cm2. Calculate content of square over the triangle's hypotenuse.
9. Iron ball The iron ball has a weight of 100 kilograms. Calculate the volume, radius, and surface if the iron's density is h = 7.6g/cm3.
10. Inscribed Cube is inscribed in the cube. Determine its volume if the edge of the cube is 10 cm long.
11. Granules Katy had two dogs. The first one ate a pack of granules a week and the other two times longer. Katka bought them two bags of granules. How long does it last for both dogs?
12. Functions f,g Find g(1) if g(x) = 3x - x2 Find f(5) if f(x) = x + 1/2
13. The factory The factory z can complete an order in 12 days, factory p in 18 days. For how many days does an order completed when the first two days work only the factory z and then both factories?
14. Triplets Three years ago, the triplets Pavel, Petr, and Luke and their five-year-old sister Jane had together 25 years. How old is Jane today?
15. Mixture How many percentages mixtures do we get by adding 23ml of matter to 89ml of water?
16. Composite ratio Jakub, Aneta, and Lenka divided 1342 USD in the ratio 5/2: 3/10: 1/4. How much did Lenka take?
17. One three We throw two dice. What is the probability that max one three falls?
18. Filament of bulb The filament of bulb has a 1 ohm resistivity and is connected to a voltage 220 V. How much electric charge will pass through the fiber when the electric current passes for 10 seconds?
19. A trapezoid A trapezoid 75 ft wide on top 85 ft on the bottom, the height is 120 ft. What is its area in the square yds?
20. Sixty Sixty percent of one-fifteen of the total is equal to thirty. What are two percent of the total?

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