IIT JEE-AIEEE 2012, Entrance Notifications, Study Tips, Engineering Preparation, Practice Test Papers, Experts Advice

Ask iit jee aieee pet cbse icse state board community

Discussion Response Post to: permutation problems plz solve

Forum Index -> Algebra -> View Full Question

Author

Message

Priyesh (1601)

Blazing goIITian

total posts: 1042
Offline

Hi Abhijeet

ans to 4)

let us consider ABCD to be in order. now we have to insert 2 people between them.

1st case: the other two persons(E&F) will be together

_ _ A _ _ B _ _ C _ _ D _ _
no.of ways ⁵C₁*2!=10 ways

2nd case : the other two persons will not be together

_ A _ B _ C _ D _

no. of ways ⁵C₂* 2!=20 ways

total ways=10+20=30

the mistake made by kvenkan was that if we insert the other people in position 1 & 5 or 2 & 5(see fig below) there is no difference in the arrangement.

12A34B56C78D910

Hope you understood

Like 0 people liked this

Free Sign Up!

Preparing for IIT-JEE ?

Arihant Revision Package for IIT JEE - Books, Practice Tests + Rank Predictor

@ INR 1,995/-

For Quick Info