here is my version of a puzzle i cud not remember but i think i can reproduce it to some extent. in case some one knows the question as well as the answer feel free to post. in a prison 21 ppl are held captive. the jailer gives them a conundrum (he happens to be the administrator of some site i cant remember-- ----*apologies* ) the condition he lays is: the prisoners can meet and plan in advance but they may not meet or be able to communicate afterwards. the prisoners will be taken to a closed room with two switches. each prisoner will have to toggle any one switch. the prisoners can be taken any number of times in any order. after any prisoner is sure that all twenty one have been given a chance to toggle the switch at least once, he may declare so and all will be freed. but if his declaration is incorrect all prisoners will be executed (cruel jailer ). can any one come up with a sure fire idea abt this. there are 21 lives at stake .