Question

Given a grid with 15 sections, determine how many sections in the grid need to be shaded so the probability of a point chosen at random in the shaded area is exactly 0.8. Explain your reasoning.

Answer 1

Probability = (shaded sections)/(total sections). Let x be the number shaded. Then x/15 = 0.8 = 4/5, so x = 15*(4/5) = 3*4 = 12.

Thus 12 sections must be shaded.