Maths-
General
Easy

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 :

  1. 42    
  2. 34    
  3. 25    
  4. 52    

hintHint:

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
    n squared space minus space n space equals space 600
n squared space minus n space minus space 600 space equals space 0
S o l v i n g space t h e space e q u a t i o n space b y space s p l i t t i n g space o f space m i d d l e space t e r m s
n squared space minus space 25 n space plus 24 n space minus space 600 space equals space 0
n left parenthesis n minus 25 right parenthesis space plus 24 left parenthesis n minus 25 right parenthesis space equals space 0
n space equals space 25 space comma space minus 24
N e g a t i v e space v a l u e space n o t space p o s s i b l e
n space equals space 25
    The number of students in the class are 25.

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