Flag Discuss with colleagues and IITians> permutation and combination...
question mark

a flight of stairs has 10 steps.a person can go up the steps one at a time ,two at a time,or any combination of 2's and 2's.find d total number f wayz in which d person can go up d stairs??? plz give me complete soln for dis....cuz i got d ans bt prob z m nt sure about the way i solved it!! ans is:89
do reply....plzz!!

shalini goyal , 14 Years ago
Grade 12
anser 1 Answers
AskiitiansExpert Mohit-IITD

Last Activity: 14 Years ago

Dear Shalini,

There are 10 steps, so following cases are possible:

10 single steps =1

1 double steps, 8 single steps = 9!/8! =9

2 double steps, 6 single steps = 8!/6!2!=28

3 double steps, 4 single steps = 7!/4!3!=35

4 double steps, 2 single steps = 6!/4!2!=15

5 double steps = 1

Total=89

Hope this helps.

Please feel free to post as many doubts on our discussion forum as you can. We are all IITians and here to help you in your IIT JEE preparation. 

Now you can win exciting gifts by answering the questions on Discussion Forum. So help discuss any query on askiitians forum and become an Elite Expert League askiitian.

star
LIVE ONLINE CLASSES

Prepraring for the competition made easy just by live online class.

tv

Full Live Access

material

Study Material

removal

Live Doubts Solving

assignment

Daily Class Assignments