# Expression of a variable from formula - examples - page 22

1. Together 3
If Sally can paint a house in 4 hours, and John can paint the same house in 6 hours, how long will it take for both of them to paint the house together?
2. Tetrahedron
What is the angle of the sides from the base of a three-sided pyramid where the sides are identical?
3. The pole
The telegraph pole is supported by a 4 m bullet at 3/4 of its height, the end of which is at a distance 2.5 m from the pole post. Calculate the height of the telegraph pole.
4. Orchard
One-eighth of the trees in the fruit plant in winter froze and one-twelfth of damaged disease and pests. Healthy trees remained 152. Is it enough to supply 35 trees to restore the original number of trees in the orchard?
5. Sugar production
From 1 ton of beet, 150 kg of sugar is produced. To clean 1 ton of sugar 450 kg of lime is consumed. Calculate how many kgs of lime is consumed when processing 1 ton of sugar beet?
6. Sale discount
The product was discounted so that eight products at a new price cost just as five products at an old price. How many percents is the new price lower than the old price?
7. Cuboid
The sum of the lengths of the three edges of the cuboid that originate from one vertex is 210 cm. Edge length ratio is 7: 5: 3. Calculate the length of the edges.
8. Cube edges
The sum of the lengths of the cube edges is 42 cm. Calculate the surface of the cube.
9. Bicycle gear
The pedal bicycle wheel has 56 teeth and a rear 20 gear tooth. How many times does the bicycle wheel turn when you make 20 turns of the pedal wheel?
10. Cube edges
If the edge length of the cube increases by 50%, how does the volume of this cube increase?
11. Two diggers
Two diggers should dig a ditch. If each of them worked just one-third of the time that the other digger needs, they'd dig up a 13/18 ditch together. Find the ratio of the performance of this two diggers.
12. Eggs
3400 eggs sliced hens for February and March. We have to calculate how many hens can make 3400 eggs when one hen give 2 eggs a day for 59 days.
13. Body diagonal - cube
Calculate the surface and cube volume with body diagonal 15 cm long.
The regular quadrangular pyramid has a base length of 6 cm and a side edge length of 9 centimeters. Calculate its volume and surface area.
15. Children playground
The playground has the shape of a trapezoid, the parallel sides have a length of 36 m and 21 m, the remaining two sides are 14 m long and 16 m long. Determine the size of the inner trapezoid angles.
From the junction of two streets that are perpendicular to each other, two cyclists (each on another street) walked out. One ran 18 km/h and the second 24 km/h. How are they away from a) 6 minutes, b) 15 minutes?
17. Inlet minus outlet
Water flows into the tank through two pipes and flows out of the third pipe spontaneously. The pipe A itself would fill the tank in 3 hours, the pipe B itself would fille in 4 hours, and the pipe C itself would flow out in 12 hours. How long will the tank.
18. Sum of squares
The sum of squares above the sides of the rectangular triangle is 900 cm2. Calculate content of square over the triangle's hypotenuse.
19. Body diagonal
Calculate the cube volume, whose body diagonal size is 75 dm. Draw a picture and highlight the body diagonal.
20. Regular prism
The regular four-sided prism has a base of 25 cm2 and a surface of 210 cm2. Find its volume.

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