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Praetorian
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anandnk
Combinations with Juliet and Romeo together = 2 * 5! = 240
Out of these the combinations with caesar and and Brutus together are invalid = 2 * 2 * 4! = 96

Total arrangements = 240-96 = 144


Wow, congrats, your solution is much simplier! :oops:
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maxpowers
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anandnk
Combinations with Juliet and Romeo together = 2 * 5! = 240
Out of these the combinations with caesar and and Brutus together are invalid = 2 * 2 * 4! = 96

Total arrangements = 240-96 = 144


How do you know the # of combinations with Romeo and Juliet together is 2*5!

Also, how did you figure out the combinations with Caesar and Brutus together that are invalid?
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Hi maxpowers,

No of people to be seated are J,R,C,B,H and P

Now J always wants to sit next to R Let si join them together and call them X
Now we have to arrange X,C,B,H,P ( I hope you agree )
There are 5 people here and can earranged in 5! ways. But that is not it.
We made X out of J and R right. J and R can be arranged as JR or RJ so we have two combinations here. Had we said only JR is allowed then there would have been 5! combinations.
Since we say RJ is also valid we have 2 * 5! ways.

But these combinations also include those in which C and B are together
So what are the ways in which J&R are together and C&B are together?
Let us call J&R as X and C&B as Y

So we have X,Y,H,P to be seated in 4! ways
But X has 2 hidden combinations as I explained above
Y also has 2 hidden combinations

In total there are 2*2*4! combinations in which J&R are together and C&B are together.

If you subtract this number from the number in whihc only J&R are together you will be left with combinations in which only J&R are together

So answer is 2*5! - 2 * 2 * 4! = 144

I hope I have explained it properly.
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Quote:
How do you know the # of combinations with Romeo and Juliet together is 2*5!

Think of Romeo and Juliet as a unit since they always will be together. So now we only have 5! positions left. Also we have 2 such situations: JR and RJ which is why we multiply by 2 giving 2 * 5!


Quote:
Also, how did you figure out the combinations with Caesar and Brutus together that are invalid?


Well, this is when Caesar and Brutus are next to each other. Like in the above example with Romeo and Juliet, think of Caesar and Brutus as a unit. So we have 6 - 2(units) = 4! positions left. The two units each have 2 different situations: JR and RJ AND CB and BC = 2* 2* 4!
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After reading both explanations I understand the solution. I have been working with Arco/Kaplan/OG problems and haven't seen many combination problems like this one so I'm a little rusty.

When I tried the problem I tried writing out 6 dashes and thinking about how many could go into each place, but after about a minute I figured out that was not the way to solve the problem. After reading your solution it makes perfect sense. Thanks again for your help.
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nice explanations everyone.

anand and ndidi made my job easier :)

144 is indeed the answer.

maxpowers, these are tougher problems. these problems will help you understand the whole concept ,rather than just one problem at a time.

Sincerely
Praet



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