# The most difficult problems

#### Number of problems found: 6440

- Angle of two lines

There is a regular quadrangular pyramid ABCDV; | AB | = 4 cm; height v = 6 cm. Determine the angles of lines AD and BV. - Ratio of sides

Calculate the area of a circle with the same circumference as the circumference of the rectangle inscribed with a circle with a radius of r 9 cm so that its sides are in ratio 2 to 7. - Equilateral triangle vs circle

Find the area of an equilateral triangle inscribed in a circle of radius r = 9 cm. What percentage of the circle area does it occupy? - Big family

A certain number of people met at the family celebration - their average age was three times the number present. Then came my grandfather, who was 75 years old and the average age was again three times the number present. How many people are celebrating r - A photograph

A photograph will stick to a white square letter with a x cm length. The photo is 3/4 x cm long and 20 cm wide than the width of the paper. The surface of the remaining paper surrounding the photograph is 990 cm^{2}. Find the size of paper and photo. - Castle model

The castle model has a cone-shaped roof. The cone side is 45 cm long and the base radius is 27 cm. a) What is the roof volume? b) How many dm^{2}of wallpaper is used to glue the roof, ie the cone shell? c) What is the weight of the roof if it is made of woo - The difference

The difference of two numbers is 1375. If their exact quotient is 12. Find the two numbers - Profit growth

The profit of a company increased by 25% during the year 1992, increased by 40% during the year 1993, decreased by 20% in the year 1994 and increased by 10% during the year 1995. Find the average growth in the profit level over the four years periods? - Athletic competition

In a 400 meter athletic competition, a participant covers the distance as given below. find the average speed? first 80 meters 10 m/s next 240 meters 7.5 m/s last 80 meters 10 m/s - Pile of sand

A large pile of sand has been dumped into a conical pile in a warehouse. The slant height of the pile is 20 feet. The diameter of the base of the sand pile is 31 feet. Find the volume of the pile of sand. - A screen

A screen is 1680 x 1050 pixels. What are the coordinates (and size in pixels) of an centered area which is exactly 33% of the screen size? - Mixing Celsius and Fahrenheit

Add up three temperatures: 5°F +6°F +0°C - Hyperbola equation

Find the hyperbola equation with the center of S [0; 0], passing through the points: A [5; 3] B [8; -10] - Coordinates of square vertices

The ABCD square has the center S [−3, −2] and the vertex A [1, −3]. Find the coordinates of the other vertices of the square. - Closed drum

Find the total surface area of a closed cylindrical drum if it's diameter is 50 cm and height is 45 cm . (π= 3.14) - KLM triangle

Find the length of the sides of the triangle KLM if m = 5cm height to m = 4.5 cm and size MKL angle is 70 degrees. - Find the sum

Find the sum of all natural numbers from 1 and 100, which are divisible by 2 or 5 - The size

The size of a Trapezium are 3/4×cm, ×cm 2(×+1)cm and 3(×+2)cm long respectively if it's perimeter is 60cm, calculate the length of each side. - Sum of dividend

If X is divided separately 2.63 and 1.40. And the results of the individual divisions are added to give a result less than X. What is X? - Unknown mixed number

Find the number that is smaller than 5 5/12 by as much as 2 2/13 is smaller than 6 1/6

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