There are ten bags containing marbles. Each bag has at least 10 marbles in it. Nine of the bags contains only marbles weighting 10 grams each. One of the bags contains only marbles weighing nine grams each. Each bag has a different number of marbles in it. All of the marbles look exactly the same. The riddle is how can you know which bag has the nine gram marbles if the only device allowed to be used is a weighing scales which you can use only once?

place all the 10 bags in sequence and mark them from 1 to 10, now take 1 marble from bag#1, 2 marbles from bag#2 and so on for the remaining bags, so that 10 marbles from bag #10. so now we have 55 marbles, so if all the marbles are of 10 gram, then total weight will be 550 grams,,, but as there are some 9 gram marbles as well,,, so its weight will be less than 550 grams. if bag#1 is of 9 gram marble bag,,, then there will be 1 9-gram marble and 54 10-gram marbles,,, showing total weight of 549 gram,,, thats mean difference in the actual and 550 gram will tell the bag number

so if difference is 1,,, then its bag#1, if diff is 2,, then bag#2 and so on

Geo brother.........mujhay umeed thi k iska jawab aap hi dogay

han na bilkul muj pe gaya hai mera bhai