# Expression of a variable from formula - examples - page 11

1. Rectangle
The rectangle has a perimeter 75 cm. Diagonal length is 32.5 cm. Determine the length of the sides.
2. Rotary bodies
The rotating cone and the rotary cylinder have the same volume 180 cm3 and the same height v = 15 cm. Which of these two bodies has a larger surface area?
3. Expressions
Expression (3a-7).(3a+7) is identical with: ?
4. Cylinder twice
If the radius of the cylinder increases twice, and the height is reduced twice, then the volume of the cylinder increases (how many times?):
5. Jam
Jar with jam weighs 800 grams. Jam weighs three times as much as the empty glass. What is the weight of jam that is in the glass?
6. Cuboid and ratio
Cuboid has dimensions in ratio 1:2:6 and the surface area of the cuboid is 1000 dm2. Calculate the volume of the cuboid.
7. Unknown number 7
16% of the unknown number is by 21 less than unknown number itself. Determine the natural unknown number.
8. Bus lines
Buses connections are started from bus stop on its regular circuit as follows: No. 27 bus every 27 minutes and No.18 every half hour. What time started this two bus lines run if the bus stop met at 10:15 am.?
9. Billboard
Rectangular billboard is 2.5 m long with a diagonal 2.8 m long. Calculate the perimeter and the content area of the billboard.
10. Even / odd numbers
a / Using variable n write two consecutive odd numbers. b / the sum of three consecutive odd numbers is 333. What are this numbers?
11. Sides ratio
Calculate the circumference of a triangle with area 84 cm2 if a:b:c = 10:17:21
12. Hollow sphere
The volume of the hollow ball is 3432 cm3. What is its internal radius when the wall thickness is 3 cm?
13. Square and rectangle
Calculate the side of a square which content area equals area of the rectangle having a length of 3 cm greater and by 2 cm smaller than the side of the square.
14. Points on circle
In the Cartesian coordinate system with the origin O is a sketched circle k /O; r=2 cm/. Write all the points that lie on a circle k and whose coordinates are integers. Write all the points that lie on the circle I / O; r=5 cm / and whose coordinates are i
15. Car consumption
The car has passed 988 kilometers and consumed 66 liters of petrol. What is the consumption per 100 kilometers?
16. Perimeter from area
What is the perimeter of the square if its content is 64 cm2?
17. 30-gon
At a regular 30-gon the radius of the inscribed circle is 15cm. Find the "a" side size, circle radius "R", circumference, and content area.
18. Cuboid - ratios
The sizes of the edges of the cuboid are in the ratio 2: 3: 5. The smallest wall have area 54 cm2. Calculate the surface area and volume of this cuboid.
19. Diagonal of the rectangle
Calculate the diagonal of the rectangle which area is 54 centimeters square and the circuit is equal to 30 cm.
20. Unknown number 24
f we add 20, we get 50% of its triple. What is this unknown number?

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