when you enter the entry on the ground floor .there are 10 elevator .
Sarah and John are best friend .
Sarah live on level 30 and it take her 1.5 min
to travel from level 30 to ground .
John live on level 20 and it him 1min to travel from level 20 to ground .
"It take Sarah 30 sec to travel from level 30 to level 20 to visitor John .
It also take 30sec for John to travel up, when he want to meet up with Sarah .( Note this don't including waiting time for elevator )
Note : Approximate waiting time for elevator is (7 and half sec).
In that tall building Mary live on level 40.
Every morning she go to shcool , she only need to take an elevator from level 40 to the ground level then go to school ( it take 2 min from level 40 to ground ).( Note this don't including waiting time for elevator )
After school she go back to the building and from the ground level she take one elevator to level 38 . ( it take 2 min from ground to level 40 ).
( Note this don't including waiting time for elevator )
This happen normaly .
Then one day after coming back from school ,
She enter the ground floor and noted
out of the 10 elevator ,six of them is broken .
Mary noted the elevator she normal use is one of them .
Note: Approximate the elevator speed for every 10 level is 30sec .
also time for elevator open or close you don't have to worrỵ
Normaly it take her 2min from ground level to travel to level 40 .
(Note this don't including waiting time for elevator )
Can anyone explain why, when six elevator broken like the case above .
It take Mary 2.5min to get there . "
Noen som har en god forklaring?gjerne på engelsk takk..
