Math practice for 13 year olds - page 67 of 413

Number of problems found: 8259

Nozzle water speed
A water spray nozzle with a cross-section of 1.5 cm² sprays water at a speed of 24 m/s. What is the speed of the current in the supply pipe whose cross-section has a volume of 18 cm²?
Michal computer saving
Michael is saving for a new computer. His parents gave him 130 euros, which was 26 percent of the total amount. He received 20 percent of the price of the computer from his grandmother, and his aunt added another 35 euros. How many euros does Michael stil
Roofer roof days
Three roofers cover a third of the roof in 10 days. In how many days would 5 roofers cover the entire roof at the same rate?
Tree watering distance
There are 10 trees in a row with the same spacing x = =3 meters. How many meters does a person travel if he waters two trees at once
Body current voltage
A current of 0.1 A can lethally affect a human body with a resistance of 3 kΩ. What voltage corresponds to this current?
Bulb voltage current
A current of 275 mA passes through the filament of a light bulb with a resistance of 800 Ω. What voltage is the bulb connected to?
Karel digit error
Carl had to multiply two two-digit numbers. Out of care, he changed the order of the digits in one of the factors and got a product that was 4,248 less than the correct result. What is the correct result? How much should Karl have earned?
Wheel peripheral speed
Calculate the peripheral speed of the number on the Wheel of Fortune if the wheel rotates within a period of 0.25 seconds and the number is written 1.5 m from the center of the wheel.
Current thermal energy
How long will it take for a current of 8 A in a resistance of 30 ohms to develop thermal energy of 3 MJ if the efficiency of converting electrical energy into heat is 90%?
Number ratio subtraction
I think two numbers. Their ratio is 5:7. If 3 is subtracted from the first and 7 from the second, then the ratio is 6:7. What number was I thinking?
Triangle sides - natural
In triangle ABC, side a = 30 cm b = 7 cm. The length of the third side in cm is a natural number. What is the least and what is the greatest length that side c can have?
Cube triangle volume
In the cube ABCDEFGH, the area of triangle ABK is √20 cm². How much cm² is the volume of ABGH in a cube if you know that K is the midpoint of edge CG?
Tetrahedron segment midpoint
The sum of the lengths of all the edges of the regular tetrahedron ABCD is 48 cm. How many cm is the segment XY if you know that X is AB's midpoint and Y is CD's midpoint?
Triangle area side
Calculate the area of an isosceles triangle ABC with a base of 10 cm and a side of 7 cm. Sketch a picture.
Trapezoid perimeter base
An isosceles trapezoid has one base twice as short as the other. Its area is 42 cm², and its height is 4 cm. Calculate its circumference if you know that the arm is 5.3 cm long.
Prism pyramid ratio
For the volumes of a perpendicular prism and a pyramid with the same base and height: A) the volumes are equal B) the volume of a pyramid is three times smaller than the volume of a prism C) the ratio of the volumes of the prism and the pyramid is 1:3 D)
Peter example solving
Peter solves 40 examples. For a correctly solved example, he receives CZK 5 from his mother. For example, in a poorly solved case, he will pay 20 CZK to his mother. After solving all the examples, he had CZK 25 more than when he started counting. How many
Banknote payment count
CZK 8,000 was paid out in fifty pieces of banknotes in denominations of CZK 100 and CZK 200. How many were there?
Triangle height line
In the right triangle KLM, the hypotenuse l = 9 cm and the perpendicular k = 6 cm. Calculate the size of the height vl and the line tk.
Building shadow height
The school building casts a shadow 16 m long on the plane of the yard, and at the same time, a vertical meter pole casts a shadow 132 cm long. Determine the height of the building.

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