As shown in the figure below, there is a $ 7 \times 7 $ grid paper where each small square has an area of $ 1 \, cm^2 $, what is the area, in $ cm^2 $, of the shaded part?
A train travels between City A to City B. There are 4 other stops in-between these two cities. How many different kinds of tickets are there? (Note: The ticket from City A to City B and City B to City A must not be the same).
In a class, 22 students take painting course, 28 students take piano course, 10 students take both courses and 5 students take none of the courses. Find the number of students in the class.
As shown in the figure below, points C and D are on segment AB. The length of AC is 6 cm longer than the length of CD. The length of BD is twice as the length of AC. How much, in cm, is BD longer than AD?
Each of the digits 1, 2, 3, 4, 5 and 6 are printed on one of the 6 cards. Choose two different cards to form a 2-digit number. List down all possible 2-digit numbers in increasing order on a sheet of paper, what is the $21^{st}$ number in the list?
The average score of Peter in several math exams is 88. On the last exam, he must get 98 in order to raise his average score to 90. How many exams has he taken in total?
How many different ways are there to place 2 identical black balls and 2 identical white balls in three different boxes A, B and C such that each box should contain at least one ball?
As shown in the figure below, there is a $ 3 \times 3 $ grid paper where each small square has an area of $ 1 cm^{2} $. Find the area, in $ cm^{2} $, of the shaded part.
The sum of the digits of a 2-digit number is equal to 9. If the 2-digit number is multiplied by 5, the sum of all digits is still 9. How many such 2-digit numbers are there?
As shown in the figure below, an ant starting from point A crawl along the path to point B. It is required that both point C and point D can only pass once, how many different paths can the ant crawl?
There are 6 persons A, B, C, D, E and F attend a meeting. Some of them shake hands with one another. In the final count up, A shakes 5 hands, B shakes 4, C shakes 3, D shakes 2 and E shakes 1. How many does F shake?