The dust in an interstellar cloud blocks blue light in the following way:
For every 1 pc light travels through the cloud, only 91.0% of the light continues. Thus, after 2 pc, 91.0% of the remaining 91.0%, or 82.81% (0.91 × 0.91 = 0.828), remains. You might initially expect that after 12.00pc, the twelve 9.00% reductions would have removed all of the blue light. How much blue light actually remains?