Permutation and combination

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papie
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#1
Report Thread starter 8 months ago
#1
A girl has 11 objects to arrange on a shelf but there is room for only 7 of them. In how many ways she can arrange 7 of the objects on shelf if her clock must be included ?
I don't know how to do this. Actually i am completely lost on Permutation and combination chapter. Really need help badly . Thanks : )
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Lej75
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#2
Report 8 months ago
#2
(Original post by papie)
A girl has 11 objects to arrange on a shelf but there is room for only 7 of them. In how many ways she can arrange 7 of the objects on shelf if her clock must be included ?
I don't know how to do this. Actually i am completely lost on Permutation and combination chapter. Really need help badly . Thanks : )
If the clock has to be included, then there are six choices left for the objects on the shelf, so you need to find how many sets of 6 items from 10 there are. Then, you need to consider how many ways any set can be arranged (permuted) on the shelf. The total number takes into account each arrangement of each set.
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papie
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#3
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#3
(Original post by Lej75)
If the clock has to be included, then there are six choices left for the objects on the shelf, so you need to find how many sets of 6 items from 10 there are. Then, you need to consider how many ways any set can be arranged (permuted) on the shelf. The total number takes into account each arrangement of each set.
is this a permutation question or combination ?
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Lej75
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#4
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(Original post by papie)
is this a permutation question or combination ?
Both, you need to consider the permutations of each combination of 7 objects
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papie
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#5
Report Thread starter 8 months ago
#5
(Original post by Lej75)
Both, you need to consider the permutations of each combination of 7 objects
okay I'll try that.
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