At the end of the first semester, the Math test in grade 5A, the number of excellent students is equal to 3/7 the total student in the class. In the middle of the second semester, 3 students get good scores in the Math test so the number of excellent students is equal 2/3 to the rest of the class. How many students have good scores in the middle of the second semester? Know that the number of 5A students is unchanged in both two semesters.

The number of marbles that Ti has is no more than 80. Red marbles are 5 times more than blue marbles. If Ti has 3 more blue marbles, then the number of red marbles is 4 times more than blue marbles. How many marbles does Ti has for each colour that the beginning?

7 fractions are given:

$\frac{7}{5};\frac{4}{13};\frac{2}{13};\frac{1}{18};\frac{7}{3};\frac{4}{5};\frac{7}{4}$

Thang has to choose 2 fractions which give the the greatest sum. Long has to choose 2 fractions which give the smallest sum. Find the sum of 4 fractions that Thang and Long choose.

Find the digit a and b so that:

$\frac{1}{3}=\frac{1}{a}+\frac{1}{b}$

There are 5 teams participating in a contest. The total score of 5 teams is 144 points. It is interesting that all 5 teams achieve one in each prize: first prize (30 points), second prize (29 points), third prize (28 points). How many more teams that achieve the third prize than first prize?

Dong had 400 000 dong. He spent $\frac{1}{5}$ the money on a storybook and $\frac{3}{10}$  on a calculator. Hơ many money did he spend altogether ?

Find a natural number which has a remainder of 100 if we take $\frac{1}{3}$of the number divided by $\frac{1}{17}$ of the number ?

Son’s current age is $\frac{1}{2}$ the difference between father’s age and son’s age. Four years ago, the son’s age is $\frac{1}{3}$ the difference between their ages. How old is father’s age when son’s age is $\frac{1}{4}$  the difference of their ages?

Square ABCD is given. Cut the square into pieces so that the remaining area is equal to the area of the given square.

The perimeter of a rectangular garden is 120 m. Then the garden is expanded as shown to become a rectangular garden. Find the area of the new section open?

A rectangular piece of land is divided into four smaller rectangles which the areas  are recorded as shown. Find the area of the last rectangle ?

At a kindergarten, each teacher looks after seven children. Later, four children moved to another kindergarder, also there are 2 more new teachers. Now, each teach looks after 5 children. At first, how many children are there in the kindergarten?  Knowing that the number of teachers is under 30?

At first the number of ducks in the pond is 5 times the number of ducks on the ground. After three ducks moving from the ground into the pond , the number of ducks in the pond is eight times the number of ducks on the ground. How many ducks are there altogether? Knowing this number is less than100?

Find the sum of different 3 – digit numbers which can be formed using by digits: 0; 2; 3; 7; 5 and divisible by 15 ?

There are 4 teams in the competition, each team has 5 friends. On the opening day, they shake hands together; each friend just shakes hands a times. If each of them only shakes hands with other teammates and did not shake hands with their own teammates, how many handshakes in total?