Question 683555
To fall down it takes 1second s.
To go up on rebound  0.9 s  (90% of the time)
To fall down 0.9 s (When it falls down t=,no change in time)
To go up and rebound II 0.9*0.9 = 0.9^2
To fall down 0.9^2 
To go up 0.9^3 
To come down 0.9^3

Hence the time taken is  1 + 2(0.9) + 2(0.9) ^2 + 2(0.9) ^3 +...