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Numerical Ability
Permutation and Combination
In a staircase, there ar 10 steps. A child is attempting to climb the staircase. Each time she can either make 1 step or 2 steps. In how many different ways can she climb the staricase?
Read Solution (Total 5)
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- possibilities are
case 1:
2 steps =5
1 steps=0
to no of arrangements=1
2 steps =4
1 steps=2
to no of arrangements= (6!)/2!*4!
2 steps =3
1 steps=4
to no of arrangements=7!/(3!*4!)
2 steps =2
1 steps=6
to no of arrangements=8!/(2!*6!)
2 steps =1
1 steps=8
to no of arrangements=9!/(8!)
2 steps =0
1 steps=10
to no of arrangements=1
total arrangements =89 (add all)
- 11 years agoHelpfull: Yes(60) No(0)
- the child can climb from 1st step to 2nd step in 1 way.
frm 1st step to 3rd step in 2 ways.
frm 1st step to 3rd step in 3 ways.
frm 1st step to 4th step in 5 ways.
thus it forms fibonacci series 1,2,3,5,8,13,21,34,55,89.
therefore she can climb 10 steps in 89 ways. - 11 years agoHelpfull: Yes(13) No(0)
- possibilities are:
2 steps 1 step number of arrangements
5 0 1
4 2 6!/(4!*2!)
3 4 7!/(3!*4!)
2 6 8!/(2!*6!)
1 8 9!/(8!)
0 10 1
total= 89 - 11 years agoHelpfull: Yes(1) No(0)
- it is
1 1 1 1 1 1 1 1 1 1 =10!/10!
1 1 1 1 1 1 1 1 2 =9!/8 !
1 1 1 1 1 1 2 2 = 8!/6!*2!
1 1 1 2 2 2 =7!/3!*3!
1 1 2 2 2 2 =6!/2!*4!
2 2 2 2 2 =5!/5!
adding we get 89 - 8 years agoHelpfull: Yes(1) No(0)
- short cut: Fibonacci series 1 2 3 5 8 13 21 34 55 89
- 8 years agoHelpfull: Yes(0) No(0)
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