# Examples for 9th grade - page 94

1. Height as diameter of base The rotary cylinder has a height equal to the base diameter and the surface of 471 cm2. Calculate the volume of a cylinder.
2. Tropical, mild and arctic How many percents of the Earth's surface lies in the tropical, mild and arctic range? The border between the ranges is the parallel 23°27 'and 66°33'.
3. Circle described The radius of the circle described to the right triangle with 6 cm long leg is 5 cm. Calculate the circumference of this triangle.
4. Triangular pyramid What is the volume of a regular triangular pyramid with a side 3 cm long?
5. Sales off The price has decreased by 20%. How many percents do I have to raise the new price to be the same as before the cut?
6. Rectangular garden The sides of the rectangular garden are in ratio 1: 2. The diagonal has a length of 20 meters. Calculate the area and perimeter of the garden.
7. Digit sum How many are three-digit numbers that have a digit sum of 6?
8. Highway tunnel The highway tunnel was built from two ends in the north-south direction. The average daily performance of the "northern party" rasters was higher than the average daily power of the "southern party" of the rasters. After 55 business days, both parties met.
9. Bricklayers Seven bricklayers will build the house in 630 days. How many bricklayers do we need to take after 150 days to complete the building for (additional) 336 days?
10. Lunch Seven classmates go every day for lunch. If they always come to the front in a different order, will be enough school year to take of all the possibilities?
11. Borrowing I borrow 25,000 to 6.9% p.a.. I pay 500 per month. How much will I pay and for how long?
12. Acid evaporation How many kilograms of water do we have to evaporate from 100 kg of 32% acid to make it 80% concentration?
13. Father 7 Father is 6 times older than his son. After 4 years, the father will only be 4 times older. What are their present ages?
14. Water reservoir One drain hole emptied the water from the tank for 20 hours, with the second drain for 30 hours. How long will the water drain from this tank if we open two drains simultaneously?
15. Clogging How much distilled water must the pharmacist add to 30g of a 30% hydrogen peroxide solution to obtain a 3% solution to clogging?
16. The big clock The big clock hands stopped at a random moment. What is the probability that: a) a small hand showed the time between 1:00 and 3:00? b) the big hand was in the same area as a small hand in the role of a)? c) did the hours just show the time between 21:00.
17. Merchant The merchant lower cost by 10% in December when it was not sold. Again in January lower cost by 20% and now costs 576 €. A. How much the goods stood originally? B, how much cost the goods after the first lowering? C, How many percents totally merchant lo
18. Last digit What is the last number of 2016 power of 2017
19. Octane value I loaded 10L 95 octane gasoline and 5L 100 octane gasoline. What is the resulting octane value of the gasoline in the tank?
20. A cylinder A cylinder 108 cm high has a circumference of 24 cm. A string makes exactly 6 complete turns around the cylinder while its two ends touch the cylinder's top and bottom. (forming a spiral around the cylinder). How long is the string in cm?

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