24like this...here black coins are on table..and grey one is placed on top
Is this solvable ??
Find no of ways by which we can stack 12 coins in a line so that each coin lies on table or on 2 coins
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UP 0 DOWN 0 0 12
12 Answers
1?
how can a coin only lie on two coins cuz then the coin below will be lying on one coin
24
1the ans. if u do
6C5 + 7C4 +8C3 + 9C2 +10 C1 +11C0
is 144 and not 154
and that seems to be the right ans. if the coins r identical
1i'm not getting the rite ans...i'm getting it as 274......i guess i've counted many combinations twice.....somebody pls correct me.....but , here's my approach
we v 12 coins....we place some of them in a line and the remainig in our hands, we place them on the coins on the table so as to satisfy the given condition....
so the combinations for (line,hand)={(12,0),(11,1)........(5,7)}...it ends here....u cant hv 4 on the line & then place the remaining
(12,0)-1
(11,1)-10
(10,2)-9C2
(9,3)-8C3+7
(8,4)-7C4+5*2+6*1*5
(7,5)-6C5+3*3+4+5*4C2
(6,6)-4
(5,7)-1+2
total=274
here's an illus for (7,5)
1this approach is wrong i think bcoz u cannot place a coin in a third row
then that coin does not lie on 2 coins but more than 2 coins