64% of the kids only bring an umbrella. Set up a system of equations: suppose x% of kids only bring raincoats, and y% only bring umbrellas. Since 8% of kids bring both, 1-8%=92% bring only one of the two, so x+y=92. Percent of kids who bring raincoats is x+8, and percent of kids bringing umbrellas is y+8. y+8=2(x+8). Solve the two equations, we get x=28, y=64. 64% kids only bring umbrellas.
