Math practice for 13 year olds - page 130 of 428

Number of problems found: 8555

Magnetite iron production
Iron is produced in a blast furnace from iron ore. The wealthiest iron ore is magnetite, which contains 45-70% iron. How much magnetite do we need to get 3 tons of iron?
Pipe thickness
The outer circumference of the tube is 32cm. Its length is 60cm, its density is 8.5g/cm³, and its weight is 9.495kg. Calculate the wall thickness of the pipe.
Iso triangle
An isosceles triangle with a base of 8 cm. Its circumference is 28 cm. Calculate the height of the triangle.
Rocks
Dana loves rocks! She has six pieces of granite, three pieces of marble, 14 pieces of sandstone, and one piece of slate. What is the ratio of sandstone pieces to marble in Dana's collection?
Salaries
The employer increased the salaries of its three employees by an average of 30 euros. One increased his salary by € 20, the other by € 45. How many euros did he raise the salary of a third employee?
Circumference - diamond
The diamond has an area of 21.6 cm square. Its height is 4 cm. What is the circumference of the diamond?
Create 2
Create word problems based on the given number sentence (300/24) - (207.60/24) = N.
A turtle 2
A turtle can walk 1/12 of a kilometer in an hour. The turtle is 1/5 of a kilometer away from a pond. How long will it take the turtle to reach the pond at this speed?
Cylinder cube percentage
Calculate the percentage of the cube volume that represents the volume of the cylinder inscribed in the cube. The cylinder's bases are circles inscribed on two opposite walls of the cube with an edge a = 14 cm.
Two companies
The two companies did work together for 100 days. The first company would do it in 150 days. How many days would the work take the second company?
Resistor voltage current
A current of 5 mA flows through a resistor with an electrical resistance of 600 Ω. What electrical voltage do we measure between the resistor terminals?
Voltage - Kirchoff laws
At a voltage of 2.5V, a current I1= 20mA flows through the resistor. What will the voltage be at the resistor's ends when the current I2= 1,2A passes through it?
Prism - right isosceles
Find the volume and surface of a prism with a height of 120 mm. Its base is a right isosceles triangle with a leg length of 5 cm.
Eva brigade earnings
Eva received money for a brigade. She saved three-fifths of the money, lent one-quarter to her sister, and bought a T-shirt for the remaining 180 CZK. How much CZK did Eva earn on the brigade?
Sphere volume formula
If V=4/3 π r³, find the value of V when r = 7, the value of r when V=113 1/7
Bronze
How much tin is in 3.6 kg of bronze if it contains 15%?
Trapezoid angle construction
Sestroj trapezoid ABCD, if a = 8cm, b = 5cm, alpha = 60 °, beta = 75 °
Manganese
Manganese bronze contains the following metals per pound: copper 0.89 lb, tin 0.10 lb, and manganese 0.01 lb. How much copper is in a shaft that weighs 235 pounds?
Face combinations
If I have 20 sets of eyes, 20 noses, and 20 months, how many unique face combinations can I make?
The diagonals
The diagonals in the diamond ABCD are 6 cm and 8 cm long. What is the perimeter of this diamond?

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