Question

Each student sends a greeting card to every other student in the class for the new year. If the total number of greeting cards sent is 600. Find the number of students in the class.​

Answer 1

Answer:

For each pair of students, there will be two cards sent (A sends to B and B sends to A). Therefore, for nC2 pairs of students, the number of cards sent = 2 x nC2 = 600 (given). => n = either 25 or -24.

Step-by-step explanation:

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Answer 2

Answer:

The number of students in the class is 25.

Given:

Total number of greeting cards sent is 600.

Each student sends a greeting card to every other student in class for new year.

To Find:
We have to find the number of students in the class.

Solution:
Let the number of student be n

Then 2 students can be selected out of n students in nC2 ways = number of pairs of students.

But for each pair of students the number of card sent is 2.

So for nC2 pair, no. of cards sent will be 2*nC2 .

It is given that, 2*nC2 = 600

$n^{2} -n-600=0\\ n=25, -24$

n cannot be negative.

Hence the number of student in the class is 25

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