# Examples for 8th grade - page 100

1. Discount The dress was discounted by CZK 115, which was 12% of the original price. What is the cost of the dress after the discount?
2. CuSO4 mixture How many grams of solid CuSO4 we have to add to 450g of 15% CuSO4 solution to produce a 25% solution?
3. Seven Seven friends agree to send everyone a holiday card. How many postcards were sent?
4. Christmas Father said: "exactly after 56 hours we will sit down to Christmas Eve table" How was and what time it was when Father said this sentence? The Christmas Eve table they sit down at exactly 6 PM hour.
5. Car driver The car driver is in town A and is scheduled to be in town B at a specified hour. If it travels at an average speed of 50km/h, it will arrive in city B 30 minutes later. But if he travels at an average speed of 70km/h, he would arrive half an hour earlier
6. Construct Construct a rhombus ABCD, if the size of the diagonal AC is 6 cm and diagonal BD 8 cm long.
7. The train The train passed the observer in the 20s and passed through a 1500m tunnel in 2 minutes. Calculate the speed (km/h) and train length.
8. First man What is the likelihood of a random event where are five men and seven women first will leave the man?
9. Two pipes How long will the pool be filled with a double supply pipe if it takes the pool to fill the first pipe by 4 hours longer and the second pipe 9 hours longer than both pipes open at the same time?
10. Peroxide How many ml 30% of peroxide (H2O2) should be poured into 100ml H2O to give a 20% solution?
11. Cone 15 The radius of the base of a right circular cone is 14 inches and it's height 18 inches. What is the slant height?
12. Together 3 If Sally can paint a house in 4 hours, and John can paint the same house in 6 hours, how long will it take for both of them to paint the house together?
13. Water tank A 288 hectoliter of water was poured into the tank with dimensions 12 m and 6 m bottom and 2 m depth. What part of the volume of the tank water occupied? Calculate the surface of tank wetted with water.
14. The pole The telegraph pole is supported by a 4 m bullet at 3/4 of its height, the end of which is at a distance 2.5 m from the pole post. Calculate the height of the telegraph pole.
15. Tetrahedron What is the angle of the sides from the base of a three-sided pyramid where the sides are identical?
16. Regular triangular pyramid Calculate the volume and surface area of the regular triangular pyramid and the height of the pyramid is 12 centimeters, the bottom edge has 4 centimeters and the height of the side wall is 12 centimeters
17. Trapezium 2 Trapezium has an area of 24 square cms. How many different trapeziums can be formed ?
18. Seamstress The seamstress cut the fabric into 3 parts. The first part was the eighth fabric, the second part was three-fifths of the fabric and the third part had a length of 66 cm. Calculate the original length of the fabric.
19. Orchard One-eighth of the trees in the fruit plant in winter froze and one-twelfth of damaged disease and pests. Healthy trees remained 152. Is it enough to supply 35 trees to restore the original number of trees in the orchard?
20. Average age The company of five people has an average age of 46 years. The average age of the first four is 43 years. How many years has the fifth member of this company?

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