Calculate:

$1-\left( 1-\frac{1}{2} \right)\times \left( 1-\frac{1}{3} \right)\times \left( 1-\frac{1}{4} \right)\times ...\times \left( 1-\frac{1}{50} \right)$

( Write the result as a/b )

A rectangle and a square are given. One side of the square is equal to the width of rectangle. The perimeter of the rectangle is bigger than the perimeter of the square by 6cm. The area of the rectangle is bigger than the area of the square by 24cm2. Find the area of the rectangle. 

A square is given. Connect the midpoint of two consecutive side together of that square we have a second square.Connect the midpoint of two consecutive side together  of the second square  we get the third square. Connect the two diagonals of the given square. Find the total area of all the triangles in the figure. Knowing that the area of the given square is 156 cm² ?

Calculate:
$\frac{6}{\text{1x}3\text{x7}}+\frac{6}{3\text{x7x9}}+\frac{6}{\text{7x9x13}}+\frac{6}{9\text{x13x}15}+\frac{6}{\text{13x}15\text{x}19}$
( Write the result as a/b )

Triangle ABC is given. Point D and E lie on side AB so that AD = ED = DB. Point H and K lie on the side AC so that AH = HK = KC. Point M and N lie on side BV so that BM = MN = NC. Knowing that the area of triangle ABC is 360cm2. Find the area of the figure DEMNKH?

 On a map with scale of 1 : 6 000 000, the distance between Hue and Vungtau is 112mm. Find this distance in real life. ( kilometer ) 

The perimeter of a rectangle school garden is 180m. The width is $\frac{2}{3}$ the length. $\frac{1}{4}$ of the school garden is used to plant flower. What is the area for planted flower ?

Hung worked 4 days. Dung worked 5 days. Nam worked 7 days. They received the total money is 2240000 dong. How much money did each person receive ? ( Each person received the same amount of money for one day. )

The daily attendance of a school for 5 school days in a week was 729; 730; 727; 725 and 724

If the number of pupils of the school is 735. Find the average number of daily absence ?

The average of teacher and 35 students is 11 years old. Knowning that the age of teacher is 36 years old more than the average age of 35 students.Find the average age of 35 students ?

How many suitable numbers are there ?

$\overline{24*6*}$   is divisible by 2; 3 and 5 ?

Two people finish a job in 48 working days. Person A takes a break after 63 days of working, while person B continues to work in the next 28 days, then they finish the job. How long does person A need to finish the job by himself?

Find a fraction that value is $\frac{1}{2}$  such that: If we add both numerators and denominators of that fraction to the same natural number, we will get fraction $\frac{11}{12}$

Given A = y + y x 2 + y x 3 + y x 4 – 456

Find y such that the value of A is 1884 ?

Calculate:

  $\frac{1}{\text{1x}3\text{x7}}+\frac{1}{3\text{x7x9}}+\frac{1}{\text{7x9x13}}+\frac{1}{9\text{x13x}15}+\frac{1}{\text{13x}15\text{x}19}$