A staircase contains 12 steps. We can climb it 1 or 2 steps. But 8th step contains a snake so we cant step on it. In how many ways can we the top? Please solve this question

• it is devided into 3 parts
  1. 1-7 step
  2. 7-9th step
  3. 9-12th step
  1-7th step can be reached in 21 ways i.e,,
  all 1's step 1 way
  (5) 1's and 1 with 2 step 6 ways in that way it is 1+6+10+4 =21 ways
  7-9 th step 1 way
  and 9-12 3 ways
  so 21+1+3=25 ways totally
• 8 years agoHelpfull: Yes(24) No(15)
• First 7 steps can be reached with
  1. all 1's(all single steps)
  2. 5 steps with single steps and one with 2 steps
  3.3's single and 2 with 2 steps
  4.1 single and 3's double
  all 1's in only one way i.e.,7!/7!=1
  5 with 1's and 1 two is 6!/5!=6
  similerly for
  3 with 1,s and 2 with 2 steps is 5!/(3!*2!)=10
  similerly we have to solve
  
• 8 years agoHelpfull: Yes(15) No(2)
• MANJUNATH , would you plz explain how it come 10 in (1+6+10+4)..plz explain
• 8 years agoHelpfull: Yes(9) No(1)
• 105 ways.
  If u want climb n steps with 1 or 2 jumps, then possible ways are = (n+1)th fibo. Number.
  
  First 7 steps can be climbed in 21 ways.
  [ since 8 th fibo. Number ].
  
  9-12 th steps ( totally 4 steps ) can b climbed in 5 ways [ 5 th Fibo. No ].
  
  So totally 21*5=105 ways.
  
  
  
• 8 years agoHelpfull: Yes(7) No(2)
• @MANJUNATH you are genius man..!!hats off..
• 8 years agoHelpfull: Yes(4) No(0)
• It is divided into 3 parts 1. 1-7 step 2. 7-9th step 3. 9-12th step
  1-7th step can be reached in 21 ways i.e,,
  All 1's step + Five 1's and 1 with 2 steps + Three 1’s and two 2 steps + One 1’s and three 2’steps
  1 way + 6 ways + 10 + 4
  In that way it is 1+6+10+4 =21 ways
  7 to 9th step 1 way
  All 1's step + one 1’s and one 2 steps
  1 way + 2 ways
  So 21 x 1 x 3 = 63 ways totally
  
• 8 years agoHelpfull: Yes(2) No(2)
• t is devided into 3 parts
  1. 1-7 step
  2. 7-9th step
  3. 9-12th step
  1-7th step can be reached in 21 ways i.e,,
  all 1's step 1 way
  (5) 1's and 1 with 2 step 6 ways in that way it is 1+6+10+4 =21 ways
  7-9 th step 1 way
  and 9-12 3 ways
  so 21+1+3=25 ways totally
• 4 years agoHelpfull: Yes(0) No(0)