# Examples for 8th grade - page 48

- Container

First day got off 1/4 water from full container, second day 1/5 of the remaining water. How many percent remain container filled? - Two pumps

The first pump fills the tank in 24 hours second pump in another 40 hours. For how long will take fill the tank if operate both pumps at the same time? - Brackets

Place one pair of brackets in expression 20-16 + 10 - 4 - 2 so that the result will be 0. - Reciprocal

It is true (prove it) that if a> b> 0: ? - Saw

Imagine that the saw blade with diameter 40 cm has one tooth colored with a different color. How long is path describing by the tip of the tooth after 15 minutes, if the blade is rotated 13365 times? - Center of gravity

In the isosceles triangle ABC is the ratio of the lengths of AB and the height to AB 10:12. The arm has a length of 26 cm. If the center of gravity T of triangle ABC find area of triangle ABT. - Medians in triangle

Median of isosceles triangle has a length 3 cm. Determine the length of its sides if its perimeter is 16 cm. - Angles

The outer angle of the triangle ABC at the vertex A is 114°12'. The outer angle at the vertex B is 139°18'. What size is the internal angle at the vertex C? - 10 pieces

How to divide the circle into 10 parts (geometrically)? - Antennas

If you give me two antennas will be same. If you give me again your two antenna I have a 5× so many than you. How many antennas have both mans? - Coffee

Coffee merchant has coffee robusta and arabica species. 1 kg Robusta worth 450 CZK, Arabica 1 kg is 300 CZK more expensive. Calculate how many kilograms of Robusta and Arabica will need to produce 30 kg of the mixture so that the mixture cost is 490 CZK p - Otto and Joachim

Otto and Joachim go through the woods. After some time Otto tire and make 15 minutes stop. Joachim meanwhile continues at 5 km/h. Otto when he set off again, first running speed of 7 km/h, but it keep only 30 sec and 1 minute must continue at 3 km/h. This. - Painters

One painter could paint a school for 7 days. The second one for 6 days. It was necessary to paint the school in two days. Next painter was invited and all worked together. How long would this painter painted the school itself? - Flowerbed

The flowerbed has a length 3500mm and a width 1400mm. How many foil is needed to covers the flowerbed? How many m^{2}of foil was consumed for its production (add 10% of the material to the joint and waste)? How many liters of air is inside the enclosure? (F - Two tributaries

Two tributaries of the pool fill it in 10 hours. One of the tributaries would fill 15 hours. How long would fill the first tributary? - Distance runner

Distance runner already climbed three fifths of the total route. Thus passed 90 km. How many km he have to stop? How long is his route? - Determine the number

Determine the number x that ?. - Chimney

Lower circumference of of the chimney is 12.57 m, top circumference is 5.655 m. The slope of the walls is 87°. Determine the height of the chimney. - Area of the cone

Calculate the surface area of the cone, you know the base diameter 25 cm and a height 40 cm. - Rectangles - sides

One side of the rectangle is 10 cm longer than second. Shortens longer side by 6 cm and extend shorter by 14 cm increases the area of the rectangle by 130 cm^{2.}What are the dimensions of the original rectangle?

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