naturally occurring rubidium consists of about 73.2% rubidium-85 (atomic mass 84.9 u) and 27.8% rubidium-87 (atomic mass 86.9 u). calculate the average atomic mass of rubidium rounding your answer to 0.1 u
You can find the average by adding rubidium-85's and -87's weights then dividing the sum by two. I'm fairly certain it's 85.9 u but I would check my work
