Tickets

maths!

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question:

Ann,Ben,Carl,Donna and Eric are friends.
They have four tickets for a concert.The order in which they sit at the concert doesn't matter.
Ben must go to the concert.
If Eric goes to the concert, Donna must go too.

List all the different groups of four who could go to the concert.Remember order doesn't matter.


HELPPPPPPPPPPPPP!!!!!!!!!!!!!!PLLZZZZZZZZ!!!!!!!!!!!!
 
"If Eric goes to the concert, Donna must go too." implies they do not all have to go to the concert.

So start with Ann going to the concert:
She can be by herself: A
She can sit with Ben: A B (order doesn't matter)
She can sit with Ben and Donna: A B D
She can site with Ben, Donna and Eric: A B D E

Note that Eric cannot sit by himself as he must always be with Donna, and likewise for her.
 
Hello, maths!

Ann, Ben, Carl, Donna and Eric are friends.
They have four tickets for a concert.The order in which they sit at the concert doesn't matter.
Ben must go to the concert.
If Eric goes to the concert, Donna must go too.

List all the different groups of four who could go to the concert.
Remember order doesn't matter.
Since Ben <u>must</u> go, we have: B _ _ _

Suppose Eric goes to the concert. .We have: B E _ _
. . If Eric goes, Donna must go, too. .We have: B E D _
. . The fourth seat can be occupied by A or C.
We have <u>two</u> possible groups: {B,E,D,A} and {B,E,D,C}.

Suppose Eric does <u>not</u> go to the concert.
. .Then the other four go to the concert: {A,B,C,D}

There are <u>three</u> possible groups: {A,B,C,D}, {A,B,D,E}, {B,C,D,E}
 
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