Answer:
40 beads
Explanation:
First, let's find the length of string that the beads will be on.
The string is originally 20 cm, but 2 cm is taken off each side.
So, the string that the beads will be on is only 16 cm now.
Each bead is 4 mm wide, so we have to convert the bead width to centimeters.
4/10=0.4
So each bead is 0.4 cm.
Now to find how many beads will fit, we have to divide the length by the width of the bead.
16/0.4=40
So, Mona will need 40 beads. Hope this helps ;)