Math practice for 13 year olds - page 197 of 422

Number of problems found: 8425

Mains voltage
How much electric current flows through the appliance with a resistance of 40kΩ, connected to the mains voltage (230 V)?
Resistance 25031
The current of 25 mA passes through the resistor with a resistance of 50Ω. How much voltage do we measure on it?
Resistance 25021
Calculate the resistance and power of the appliance through which a current of 20mA flows at the mains voltage (230 V).
Electric 25011
How much voltage do we measure on a 400Ω resistor when an electric current of 55 mA passes through it?
Divide 25001
Divide 25 pairs of socks in a ratio of 2:3:5
Double ratio
The mobile phone was twice gradually discounted in the ratio of 3:2 and one-half: five-quarters. If the price was CZK 4,200 after a double discount, how much did it initially cost?
Five combers
Five combers harvest 12 rows of strawberries in 4 hours. How many rows of strawberries will two combers harvest in 10 hours?
Copper Cu wire
Copper wire with a diameter of 1 mm and a weight of 350 g is wound on a spool. Calculate its length if the copper density is p = 8.9 g/cm cubic.
Calculate
Calculate a sphere's volume and surface area with a diameter of 15 m.
Percentage 24931
There is a cylinder with the largest possible volume in the cube with an edge of 6 m. What percentage of the volume of a cube has the volume of a cylinder?
Kilogram 24921
Dahlia cooks with her mother's apple slices. They mixed flour, sugar, and butter in a ratio of 10:3:2. How many grams of sugar and butter did they put in half a kilogram of flour?
Athletics 24911
The sports class is attended by athletes, cyclists, and football players. The number of athletes to cyclists is in the ratio 3:5, football players to cyclists 1:3. How many athletes attend the class if 9 children are involved in athletics?
Cable car
The cable car will carry 1280 passengers in 40 minutes. How many people will be transported in 2.5 hours?
The field
Three tractors plow the field in 6 hours. However, after 2 hours, one tractor broke down. How long will the field be plowed?
Calculate 24881
Calculate a sphere's volume and surface area with a radius of 23dm.
Eight
Eight small Christmas balls with a radius of 1 cm have the same volume as one large Christmas ball. What has a bigger surface: eight small balls or one big ball?
Ball screen
The diameter of the ball screen is 30 cm. If we add 5% of the material to be sewn, how many m² of fabric do we need to make?
Three-digit numbers
We have digits 0, 1, 4, and 7 that we cannot repeat. How many three-digit numbers can we write from them? You can help by listing all the numbers.
Four-digit numbers
Find four-digit numbers where all the digits are different. For numbers, the sum of the third and fourth digits is twice the sum of the first two digits, and the sum of the first and fourth digits is equal to the sum of the second and third digits. The di
The circumference
The circumference and width of the rectangle are in a ratio of 5:1. Its area is 216 cm². What is its length?

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