there are 1000 doors that are of the open-close type. When a person opens the door he closes it and then opens the other. When the first person goes he opens-closes the doors ion the multiples of 1 i.e., he opens and closes all the doors. when the second goes he opens and closes the doors 2, 4 6 8 resly. Similarly when the third one goes he does this for 3 6 9 12 15th doors resly. Find number of doors that are open at last.
RE: there are 1000 doors that are of the open-close ty...
Ans: 334
For Every 30 doors 10 doors will be left open(as mutilpes of 2 and mutilples of 3 are only closed remaining numbers will be 10).
So like that for every 300 doors 100 doors willbe left open.
For 900 doors 300 doors willbe left open.
And in the remaining 100 doors 34 doors willbe left open(as for 30 doors 10 doors are left open so for 90 doors 3o doors will be left open and among the remaining 10 doors 4 doors are left open).
RE: there are 1000 doors that are of the open-close ty...
hi
the question was at last how many doors will be open. but the question makes clear that when each door is opened it is closed immediately so at the last all doors will be closed irrespective of in which thw doors are opened.
RE: there are 1000 doors that are of the open-close ty...
if doors are one after the other like in a tunnel 667first person closes all the doors.second one closes 2 4 6...third one to go through opens the door if it was previously not opened. But closes only 3 6 9..999. >closes 333 doors. And leaves open 664 doors.or0 if they are at the same level. since everybody closes the door they opened.
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