# The most difficult problems

#### Number of problems found: 5745

- 15 teachers

15 teachers teach for a combined amount of 128 days over a period of 64 days. What is this expressed as a percentage? - Rectangles

The perimeter of a rectangle is 90 m. Divide it into three rectangles, the shorter side has all three rectangles the same, their longer sides are three consecutive natural numbers. What is the dimensions of each rectangle? - Cube, cuboid, and sphere

Volumes of a cube and a cuboid are in ratio 3: 2. Volumes of sphere and cuboid are in ratio 1: 3. In what ratio are the volumes of cube, cuboid, and sphere? - Evaluation of expressions

If a^{2}-3a+1=0, find (i)a^{2}+1/a^{2}(ii) a^{3}+1/a^{3} - Taxi

A taxi ride costs $3 plus $2.50 per mile. Write and Graph an equation in two variables that represents the total cost of a taxi ride. - Cancel fractions

Compress the expression of factorial: (n+6)!/(n+4)!-n!/(n-2)! - Normal distribution GPA

The average GPA is 2.78 with a standard deviation of 4.5. What are students in the bottom the 20% having what GPA? - Overload

What overload in g (g-force) has passed the pilot if he accelerated from 0 to 600 km/h in 3 seconds? - The Scout Tent

The Scout Tent has a rectangular wooden underlay with dimensions of 220 cm and 150 cm. How much canvas is needed for a 170 cm high of pyramid roof? - Hypotenuse - RT

A triangle has a hypotenuse of 55 and an altitude to the hypotenuse of 33. What is the area of the triangle? - Thunderstorm

The height of the pole before the storm is 10 m. After a storm when they come to check it they see that on the ground from the pole blows part of the column. Distance from the pole is 3 meters. At how high was the pole broken? (In fact, a rectangular tria - Hexagon ABCDEF

In the regular hexagon ABCDEF, the diagonal AE has a length 8cm. Calculate the circumference and the hexagon area. - The sides

The sides of a rectangle are in a ratio of 2:3, and its perimeter is 1 1/4 inches. What are the lengths of its side? Draw it. - Right angled triangle 3

Side b = 1.5, hypotenuse angle A = 70 degrees, Angle B = 20 degrees. Find its unknown sides length. - Water flow 2

How many litres of water will flow in 7 minutes from a cylindrical pipe 1 cm in diameter, if the water flows at a speed of 30 km per hour - Train speed

Two guns were fired from the same place at an interval of 10 minutes and 30 seconds, but a person in a train approaching the place hears second shot 10 minutes after the first. The speed of the train (in km/hr), supposing that sound travels at 340 m/s is: - Exponential warm

Suppose that a body with temperature T1 is placed in surroundings with temperature T0 different from that of T1. The body will either cool or warm to temperature T(t) after time t, in minutes, where T(t)=T0 + (T1-T0)e^(-kt) . If jello salad with 30 degree - Diagonal to area

Calculate the area of a rectangle in which the length of the diagonal is 10 cm. - Curve and line

The equation of a curve C is y=2x² -8x+9 and the equation of a line L is x+ y=3 (1) Find the x co-ordinates of the points of intersection of L and C. (2) Show that one of these points is also the stationary point of C? - Radioactive material

A radioactive material loses 10% of its mass each year. What proportion will be left there after n=6 years?

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