First slide

Permutations

Question

In a network of railways, a small island has 15 stations. The number of different types of tickets to be printed for each class, if every station must have tickets for other station, is

Moderate

A

230
B

210
C

340
D

None of these

Solution

For each pair of stations, two different types of tickets are required, Now, the number of selections of 2 stations from 15 stations $= 15 \times 14$ .
$∴$ Required number of types of tickets $= 15 \times 14 = 210$

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