Because abc is a prime number,the number of divisors of abcabc is :

(1 + 1)4 = 16

You should check the question.This problem is easy

ab - ba = 0,so n2 = 0.Then n = 0

The difference between 2 square numbers in the question is : 
(n + 19) - (n - 6) = 25

So those square numbers must be 0 and 25.Then that number is 6

To use the smallest number of tiles,the size of each tile must be the largest.Let x (cm) be that size,so we have x = GCD(30 ; 45) = 15

=> y = 30 x 45 : 152 = 6

5460 = 22 x 3 x 5 x 7 x 13

=> GCD (3432 ; 5460) = 22 x 3 x 13 = 156

1998 = 2 x 33 x 37,then 1998 has : (1 + 1)(3 + 1)(1 + 1) = 16 (factors)

So x = 16

P/S : 16 is the number of positive factors of 1998,so 1998 has 32 integer factors

Let a,b,c be the number of the correctly answered questions , unanswered questions , incorrectly answered questions of a participant respectively

Then the participant's total score is 5a + b - c with a + b + c = 30

If a is odd,then 5a and b + c are odd,so b - c is odd and 5a + b - c is even

If a is even,then 5a and b + c are even,so b - c is even and 5a + b - c is even

From 2 cases,we know that the total score of all participants is always an even number

22009 is even number 

32009 = 34.502 . 3 = .....1 . 3 = ......3 (odd number)

72009 = 74.502 . 7 = .....1 . 7 = .....7(odd number)

 = 94.502 . 9 = ......1 . 9 = .......9(odd number)

So : 22009 + 32009 + 72009 + 92009 =  .....2 + .....3 + ....7 + .....9 = ......21 (odd number)

We have :

22009 is even number 

32009 = 34.502 . 3 = .....1 . 3 = ......3 (odd number)

72009 = 74.502 . 7 = .....1 . 7 = .....7(odd number)

 = 94.502 . 9 = ......1 . 9 = .......9(odd number)

So : 22009 + 32009 + 72009 + 92009 =  .....2 + .....3 + ....7 + .....9 = ......21 (odd number)

Let a (cm) be the largest possible square size

=> a = GCD (140 ; 240) = 20 

So the largest size of the square's edge is 20 cm.Then the smallest number of squares can be cut from the cardboard is :

140 x 240 : 202 = 84

Answer : 20 cm ; 84 squares

The odd number between the six remaining numbers is:

1337 : 7 = 191

So 7 consecutive numbers are 185 ; 187 ; 189 ; 191 ; 193 ; 195 ; 197

Because the lowest common multiple of a and b is 50 . So all possible values of a and b is :

(a;b) = {1 ; 2 ; 5 ; 10 ; 25 ; 50}

The sum of the equal parts is:
       3 + 8 = 11 (part)
Baby number is:
      198: 11 x 3 = 54
Large numbers are:
       198 - 54 = 144
           Answer: SB: 54
                          SL: 144

The number of terms is:
(200 - 1): 1 + 1 = 200 (number)

We have:
From 1 to 9 have a two digit number
From 10 to 100 has 19 digits two
From 101 to 200 there are 20 digits two
So 1 to 200 are: 1 + 19 + 20 = 40 digits 2
Is is : 200 - 40 = 160 with no 2 digits

Answer: 160