Question 505180
If you ride the escalator, you travel 1/30th the distance to the top per sec
If you walk up the stairs you travel 1/20th the distance to the top per sec.
If you do both then you travel 1/30 + 1/20=1/12 the distance to the top per sec.
Sooooo, doing both it takes 12 seconds to reach the top.

another way:

Let x=time it takes to both ride the escalator and walk at the same time
Then (1/12)x=1( complete distance to top, that is)
x=12 sec

Hope this helps---ptaylor