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Question

There are 40 persons in a palace. If every person shakes hands with every other person, what will be the total number of handshakes?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
780

Problem Analysis: Total Handshakes

This problem involves calculating the total number of unique pairs that can be formed from a group of 40 individuals, where each pair represents a handshake. Since the order of people in a handshake does not matter (Person A shaking Person B's hand is the same handshake as Person B shaking Person A's hand), this is a combination problem.

Applying the Combination Formula

The number of combinations of choosing k items from a set of n items is given by the formula:

$C(n, k) = \frac{n!}{k!(n-k)!}$

For the handshake problem, we are choosing groups of 2 people (k=2) from a total of 40 people (n=40). The formula simplifies to:

$C(n, 2) = \frac{n(n-1)}{2}$

Calculation for 40 Persons

Given n = 40 persons:

  • Substitute the value of n into the simplified formula:

    $C(40, 2) = \frac{40 \times (40 - 1)}{2}$

  • Perform the subtraction:

    $C(40, 2) = \frac{40 \times 39}{2}$

  • Simplify the expression:

    $C(40, 2) = \frac{1560}{2}$

  • Calculate the final result:

    $C(40, 2) = 780$

Therefore, the total number of handshakes will be 780.

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