Exercise #4
1 answer:
You might be interested in
As there are 3 couples, so that means there are total 3 × 2 = 6 people altogether.
So now to make 6 people sit on 6 sits can be done in folowing ways:
suppose these are 6 seats available
_____1__ ______2___ ____3______ ___4__ ____5___ ___6____
Now there are 6 ways to make a person sit on seat 1.
Once seat 1 is occupied we are left with 5 people (1 person sat on seat 1)
so now 2nd seat can be filled in 5 ways
after 1 person sat on seat 2, then 3rd seat can be filled in 4 ways ( out of 6 people already 2 people sat on seat 1 and 2 so only 4 people left for 3rd seat)
And similarly for 4th seat can be filled in 3 ways
then 5th seat can be filled in 5 ways
then 6th seat can be filled in only 1 way.
Now as per fundamental principle of counting if there are m ways to do one event and n ways to do another event so altogether are m × n ways to do them.
So using same fundamental principle of counting here we get total ways to make 6 people sit on 6 seats as 6 × 5 × 4 × 3 × 2 × 1 or 6! = 720 ------------(1)
----------------------------------------------------------------------------------------------------
Now they want each couple to sit together. So every two particular people make one group (1 couple).
so like we saw 6 people can be seated on 6 seats in 6! ways (from (1))
similarly 3 couples can be seated in 3! or 3 × 2 × 1 = 6 ways
And 1st couple can sit in 2 ways amoung themselves (husband left wife right or wife left and husband right).
similarly 2nd couple can also sit in 2 ways amoung themselves
and 3rd couple can also sit in 2 ways amoung themselves
So altogether, by funadmental principle of counting, all 3 couples can be seated in 6 × 2 × 2 × 2 = 48 ways -----------(2)
--------------------------------------------------------------------------------------------
Probability of event is given by formula:
so favourable outcomes from (2) we have as 48
total number of outcomes from (1) we have 720.
so plug these value in probability formula
Probability =
To reduce this fraction divide by greatest common factor in 48 and 720 which is 48. so we get
so thats the final answer.