Question

There are 20 persons among whom two are sisters. Find the number of ways in which we can arrange them around a circle so that there is exactly one person between two sisters? Please note that the exact position on the circle does not matter (no seat numbers are marked on the circle), and only the relative positions of the people matter. *

Answer 1

Answer:

18!

Step-by-step explanation:

• Given  
• There are 20 persons among whom two are sisters. Find the number of ways in which we can arrange them around a circle so that there is exactly one  person between two sisters?
• First let the two sisters be arranged around a circle in such a way that there will be one seat vacant between them.
• Since the arrangement of the sisters is not circular this can be done in 2! ways.
• Then the other 18 people can be arranged on 18 seats in 18! ways.