Examples for 8th grade - page 21
- Common chord
Two circles with radius 15 cm and 11 cm are intersect at two points. Its common chord is long 20 cm. What is the distance of the centers of these circles?
- Four-digit number
Find also a four-digit number, which quadrupled written backwards is the same number.
Annie aunt is 35 years old, Annie is 14 years. For how many years will aunt have twice as many years as Annie?
First painter painted fence himself for 12 hours, the second painter 3 hours sooner than first, and the third painters slowest up to 20 hours. How long took them paint fence if worked together?
How much metal is needed for production 37 pieces of gutter pipes with the diameter 16 cm and length of 1 m? The plate bends add 7% of the material.
Pool is filled with two water supply. The first supply fill pool for nine hours, the second for six hours. How many hours will take fill the pool when the water flows in through the first supply 3 hours and then we will open a second supply?
Dog is tied to a chain, which is mounted in a corner of the yard. Yard has the shape of a square with a side length of 20 meters. The same long is also dogchain. Are there places in the yard where dog can't reach?
- Hockey match
The hockey match ended with result 3:1. How many different storylines may have the match?
Two members will make profit 52 000, - EUR. The forst earned 8% more and the second 10% more and thus earned together 56 700, - EUR. How many will initially each earn?
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?
- Tank and water
Cylindrical tank were poured with 3.5 liters of water. If tank base diameter is 3 dm, how height is water level in?
Bottle with wine costs 61 USD. Wine is 11 USD more expensive than the empty bottle. How much is the bottle itself?
Workers A and B will done work together for 20 days. They worked together 18 days. Then A worker became ill and worker B finish the job alone for 11 days. If every worker was working alone, how many days took whole work for worker A and B?
- Quarter circular
The wire that is hooked around the perimeter of quarter-circular arc has length 14π+56. Determine the radius of circle arc.
Two gears, fit into each other, has transfer 1:5. Centres of gears are spaced 28 cm. What are the radii of the gears?
How many 20-cent coins must be put in a row that next 20-cent coins after them (above) rolled on it axis?
Forest has an area of 36 ha. How much area is occupied by forest on the map at scale 1:5000?
- Maximum area of rhombus
Calculate the interior angles at which equilateral rhombus has maximum area.
- Chocholate pyramid
How many chocolates are in the third shelf when at the 8th shelf are 41 chocolates in any other shelf is 7 chocolates more the previous shelf.
Six tractors plowing the field for 8 days. After two days, two tractors broke down. How many days were prolonged work in the field?