Cho hình vẽ bên: Hình có 8 cạnh, nối 2 đỉnh không cùng thuộc một cạnh thì được một đường chéo. Hỏi có bao nhiêu đường chéo?

The sum of two numbers is 700. If the greater is decreased by 28 units, the greater is 20 units more than the smaller. Find the greater number?

Two bookshelfs have total 540 books. If Lan transfers 35 books from the second bookshelf to the first bookshelf, the others books of the second bookshelf is 108 books less than the first bookshelf. How many books are there in the first bookshelf at first ?

Find two numbers know that the greater number is 40 units more than the smaller number. If the smaller number is increased by 15 units, the sum of two numbers is 335 ? 

Two buckets contain total 82 liters. If transfering 7liters from the first bucket to the second bucket, two buckets have an equal amount of liters. How many liters does each bucket have ?

The sum of two classes 4A and AB is 86 students. Iff transfering 3 students from 4A to 4B, the students of two classes is an equal number of students . Find the number students of two classes 4A and 4B ?

Nam and Minh have total 52 marbles . If Nam give for Minh 4 marbles, Nam will be 12 marbles less than Minh. How many marbles do each person have?

Two buckets have total 155 kilograms. If the first bucket is increased by 8 kilograms and the second bucket is increased by 17 kilograms, two buckets have an equal amount of kilograms. How many kilograms are there in each bucket ?

Two bookshelfs have total 450 books. If Lan transfers 78 books from the second bookshelf to the first bookshelf, the others books of the second bookshelf is 28 books less than the first book. How many books are there in the first bookshelf at first ?

Two baskets have total 55 apples. If John transfers 10 apples from the first basket to the second basket, the number of apples in the second basket is 21 apples less than the first basket. How many apples are there in the first basket at first ?

An and Linh have total 42 marbles . If An gives for Linh 1/4 the number of An’s marbles , two person will have an equal amount of marbles . How many marbles do each person have?

Lyn’s bucket and Bell’s bucket have total 180 eggs. Bell transfers 14 eggs to Lyn’s bucket then Lyn will have 48 eggs more than Bell. How many eggs does Lyn have at first ?

An’s house and Minh’s house have total 140 ducks. If An’s house gives 22 ducks for Minh’s house, the number ducks of An’s house equals 2/5 Minh’s house. How many ducks are Minh’s house more than An’s house ?

Huy divides his apples into 2 buckets : blue bucket and red bucket. Know that the number of apples in blue bucket is 5 times more than red bucket. If Huy transfers 20 apples from blue bucket to red bucket , two buckets will have an equal amount of apples. How many apples does Huy have total at first ?

Two classes 5A and 5B have total 90 students. Teacher transfers 5 students from 5B to 5A, two classes will have an equal amount of students. How many students does each class have ?