11=21
no of ways in which a person can walk up a stairway which has 7 steps if he can take 1 or 2 steps up d stairs at a time is:
A rhombus has sides of length 10cm. a circle with centre A passes through C & similarly a circle with centre B passes through D . if d 2 circles r touching each other den d area of rhombus is =?
-
UP 0 DOWN 0 0 3
3 Answers
1look possible sets are
all 1
five 1steps n one 2 steps
three 1 steps n two 2 steps
1one 1 step n three two steps
no of ways steps can be taken r
1+6(6!/5!)+10(5!/3!2!)+4(4!/3!)=21