Hello!
For this you have to find the amount of every color of beads.
300 * 0.30 which is 90 black beads
300 * 0.25 is 75 red beads
300 * 0.15 is 45 white beads
Then you add them.
90+75+45 = 210
Then subtract them from the total
300 - 210 = 90
The answer is 90 blue beads or 30%
Hope this helps!