Let's denote:
N=80 as the total number of steps on the escalator.
s as the speed of the escalator in steps per second.
Alice's Journey:Alice's speed relative to the escalator:
Va =2 steps/second (upward).
Alice's effective speed relative to the ground:
Va,eff = Va +s = 2+s steps/second (since she walks in the same direction as the escalator).
Time taken by Alice to reach the top:
tA = N / (Va,eff) = 80/ (2+s) seconds.
Number of steps Alice walks on the escalator:
nA =Va × tA =2× 80/ (2+s) = 160 /(2+s)
Bob's Journey:Bob's speed relative to the escalator: Vb =3 steps/second (downward).
Bob's effective speed relative to the ground:
Vb,eff = Vb −s=3−s steps/second (since he walks against the escalator).
For Bob to reach the bottom, Vb >s, so 3>s.
Time taken by Bob to reach the bottom:
tB = N/ Vb,eff = 80/ (3-s) seconds.
Given Condition:
Bob takes four times as long as Alice:
tB =4×tA
By solving , we get: s=2 steps per second.
Now we ca calculate tA and nA :
By solving: tA= 20 Sec ; nA= 40 steps
So, the number of steps Alice would have walked on the escalator by the time she reaches the top is n=40.When Alice and Bob Meet:Let t be the time when Alice and Bob meet.
In time t, Alice covers a distance of (2+s)t steps from the bottom.
In time t, Bob covers a distance of (3−s)t steps from the top.
When they meet, the sum of the distances they covered must equal the total length of the escalator.
(2+s)t+(3−s)t=N
Substitute s=2:
(2+2)t+(3−2)t=80
4t+1t=80
5t=80
t = 80/5 =16 seconds.
So, the time after which Alice and Bob meet is t=16 seconds.
Final Answer: t= 16 sec & n= 40 steps