Actually, never heard it before and it took some thinking to figure it out
. I would label all the bags 1-5, then take out the same number of beads as the label on the bag said. Then place all 15 beads on the scale. Since most beads weigh 10 kgs, the weight should be close to 150 kg. But since at least one will weigh 9 kg, just subtract the actual weight from 150 and the number you have will tell you which bag contains the 9 kg beads
.
(i.e. If it was bag three then three beads would weigh 9 kg and the other 12 would be 10 kg beads from the other bags. 12x10= 120(kg). 3x9= 27(kg). 120+27= 147(kg). 150-147= 3, the number of the bag from whence the 9 kg beads came from
)
...
. It's something very small or has little value, or something like that 
.
