Question

# On a new year day every student of a class sends a card to every other student. The postman delivers 600 cards. The number of students in the class are :

- 42
- 34
- 25
- 52

Hint:

### For example there are 2 students A and B, A will give card to B and vice versa.

Thus each student will give card to other students except himself.

## The correct answer is: 25

### Total cards delivered = 600

Lets assume number of students = n

Each students will give card to (n-1) students

{(n-1),(n-1),(n-1) ............ (n-1)} n times

Total cards = n(n-1) = 600

The number of students in the class are 25.

### Related Questions to study

### A tangent to the ellipse x^{2} + 4y^{2} = 4 meets the ellipse x^{2} + 2y^{2} = 6 at P and Q. The angle between the tangents at P and Q of the ellipse x^{2} + 2y^{2} = 6 is

### A tangent to the ellipse x^{2} + 4y^{2} = 4 meets the ellipse x^{2} + 2y^{2} = 6 at P and Q. The angle between the tangents at P and Q of the ellipse x^{2} + 2y^{2} = 6 is

### An ellipse has OB as a semi – minor axis, F, F¢ are its foci and the angle FBF¢ is a right angle. Then the eccentricity of the ellipse is

### An ellipse has OB as a semi – minor axis, F, F¢ are its foci and the angle FBF¢ is a right angle. Then the eccentricity of the ellipse is

### The equation of the tangents drawn at the ends of the major axis of the ellipse 9x^{2} + 5y^{2} – 30y = 0 is

### The equation of the tangents drawn at the ends of the major axis of the ellipse 9x^{2} + 5y^{2} – 30y = 0 is

### For the ellipse 3x^{2} + 4y^{2} – 6x + 8y – 5 = 0

### For the ellipse 3x^{2} + 4y^{2} – 6x + 8y – 5 = 0

### If S’ and S are the foci of the ellipse and P (x, y) be a point on it, then the value of SP + S’P is

### If S’ and S are the foci of the ellipse and P (x, y) be a point on it, then the value of SP + S’P is

### The eccentricity of the curve represented by the equation x^{2} + 2y^{2} – 2x + 3y + 2 = 0 is

### The eccentricity of the curve represented by the equation x^{2} + 2y^{2} – 2x + 3y + 2 = 0 is

### The foci of the ellipse 25 (x + 1)^{2} + 9 (y + 2)^{2} = 225 are

### The foci of the ellipse 25 (x + 1)^{2} + 9 (y + 2)^{2} = 225 are

### The eccentricity of the ellipse 9x^{2} + 5y^{2} – 30y = 0 is

### The eccentricity of the ellipse 9x^{2} + 5y^{2} – 30y = 0 is

### The sum of all possible numbers greater than 10,000 formed by using {1,3,5,7,9} is

### The sum of all possible numbers greater than 10,000 formed by using {1,3,5,7,9} is

### Number of different permutations of the word 'BANANA' is

**In this question, one might think that the total number of permutations for the word BANANA is 6!**

This is wrong because in the word BANANA we have the letter A repeated thrice and the letter N repeated twice.

### Number of different permutations of the word 'BANANA' is

**In this question, one might think that the total number of permutations for the word BANANA is 6!**

This is wrong because in the word BANANA we have the letter A repeated thrice and the letter N repeated twice.

### The number of one - one functions that can be defined from into is

### The number of one - one functions that can be defined from into is

### Four dice are rolled then the number of possible out comes is

### Four dice are rolled then the number of possible out comes is

### The number of ways in which 5 different coloured flowers be strung in the form of a garland is :

### The number of ways in which 5 different coloured flowers be strung in the form of a garland is :

### Number of ways to rearrange the letters of the word CHEESE is

### Number of ways to rearrange the letters of the word CHEESE is

### The number of ways in which 17 billiard balls be arranged in a row if 7 of them are black, 6 are red, 4 are white is

We cannot arrange the billiards balls as follows:

There are 17 balls, so the total number of arrangements = 17!

This is incorrect because this method is applicable only when the balls are distinct, not identical. But, in our case, all the balls of the same color are identical.

### The number of ways in which 17 billiard balls be arranged in a row if 7 of them are black, 6 are red, 4 are white is

We cannot arrange the billiards balls as follows:

There are 17 balls, so the total number of arrangements = 17!

This is incorrect because this method is applicable only when the balls are distinct, not identical. But, in our case, all the balls of the same color are identical.