As given,
The diameter of one glass bead = 0.4 cm
As the beads are stringed/attached end to end that means a straight line of beads (diameter) can be imagined and adding up all the diameters or multiplying the diameter with total number of beads, we can get the total length of the necklace.
Hence, the length can be found as =
cm
or converting this in meters we get meter
Hence, the necklace will me 40 meters long.