# Examples for 8th grade - page 19

- Lock

Combination lock will open when the right choice of 3 numbers (from 1 to 25 inclusive) is selected. A. How many different lock combinations are possible? B. Is he combination lock named appropriately? - Lines

Five bus lines runs at intervals 3, 6, 9, 12, 15 minutes. In the morning, suddenly start at 4:00. After how many minutes the bus lines meet again? - Purchase

Mother bought 5 boxes of milk and 7 kg of potatoes and paid a total CZK 147. Aunt bought 7 boxes of milk and 3 kg of potatoes and paid 131 CZK. What is the price of one carton of milk and 1 kg of potatoes? How CZK together would have saved if bought at the - Electronics: Resistors in parallel

From relation for calculating the resistance of parallel combination of resistors: ? Calculate the R, if R_{1}= 2Ω a R_{2}= 15Ω - Height difference

What height difference overcome if we pass road 1 km long with a pitch21 per mille? - Cyclist

A cyclist is moving at 35 km/h and follow pedestrian who is walking at speed 4 km/h. Walker has an advantage 19 km. How long take cyclist to catch up with him? - Fertilizer

Mr. Gherkin use for fertilization 8% solution of fertilizer. 4 liters of it still left. How much water must be added to the solution to make only 4% solution? - Hexagonal prism

The base of the prism is a regular hexagon consisting of six triangles with side a = 12 cm and height va = 10.4 cm. The prism height is 5 cm. Calculate the volume and surface of the prism! - Hiker

Hiker went half of trip the first day, the third of trip the second day and remaines 15 km. How long trip he planned? - Train from Prague

First train from Prague started at 8:00 hour at 40 kilometers per hour. Train from Ostrava started at 9:20 at 80 km per hour. In how many hours and how far from cities with trains meet if the distance of cities is 400 km. - Circle in rhombus

In the rhombus is inscribed circle. Contact points of touch divide the sides to parts of length 22 dm and 9 dm. Calculate the circle area. - Dices

We will throw two dice. What is the probability that the ratio between numbers on first and second dice will be 1:2? - Pizza master

Master says that he can splits pizza to 16 parts by five equals straight cuts. Is it possible? - Cuboid

Find the cuboid that has the same surface area as the volume. - Water tank

Water tank shape cuboid has a width of 3.1 m and length twice larger. How high will reach water if water flow into 13 liters of water per second during 16 minutes? - Two workers

The first worker completed the task by himself in 9 hours, the second in 15 hours. After two hours of joint work left first worker to a doctor and the second finished the job himself. How many hours worked second worker himself? - Balance

The rod are 1.9 m long hanging weights 4 kg and 1 kg on ends. Where are centre of rod (distance from weight 4 kg) to be in balance? - Glass mosaic

How many dm^{2}glass is nessesary to produc 39 slides of a regular 6-gon, whose side has length 23 cm? Assume that cutting glass waste is 12%. - Workers

Workers digging a jump pit in the school yard. Pit has a cuboid shape with a length 12 m, a width 20 dm and depth 36 cm. They excavate 0.4 cubic meters of soil an hour. How much time (hours and minutes) is need to the excavate this pit? - Box

Calculate the angle between box base 9 x 14 and body diagonal length 18.

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