How many number of different signals can be generated by arranging atleast 2 flags in order (one below the other) on vertical staff, if 4 different flags are available?
How many number of different signals can be generated by arranging atleast 2 flags in order (one below the other) on vertical staff, if 4 different flags are available? Correct Answer 60
Concept:
Fundamental principal of multiplication:
Let us suppose there are two tasks A and B such that the task A can be done in m different ways following which the second task B can be done in n different ways. Then the number of ways to complete the task A and B in succession respectively is given by: m × n ways
Fundamental principal of addition :
Let us suppose there are two tasks A and B such that the task A can be done in m different ways and task B can be completed in n ways. Then the number of ways to complete either of the two tasks is given by: (m + n) ways.
Calculation:
Here, a signal can have either 2 flags, 3 flags or 4 flags.
Case – 1: When the signal has 2 flags one below the other on a vertical staff.
The number ways to fill the 1st vacant place = 4
The number ways to fill the 2nd vacant place = 3
∴ No. of ways to generate a signal with 2 flags = 4 × 3 = 12.
Case – 2: When the signal has 3 flags one below the other on a vertical staff.
The number ways to fill the 1st vacant place = 4
The number ways to fill the 2nd vacant place = 3
The number ways to fill the 3rd vacant place = 2
∴ No. of ways to generate a signal with 3 flags = 4 × 3 × 2 = 24
Case – 3: When the signal has 4 flags one below the other on a vertical staff.
The number ways to fill the 1st vacant place = 4
The number ways to fill the 2nd vacant place = 3
The number ways to fill the 3rd vacant place = 2
The number ways to fill the 4th vacant place = 1
∴ No. of ways to generate a signal with 4 flags = 4 × 3 × 2 × 1 = 24
Hence, total no. of signals that can be generated = 12 + 24 + 24 = 60