Calculating Weighted Average

Calculating Weighted Average

I have a table of people with an age and a value. I need to calculate the weighted Age of these rows, where "Value" is the weight. 
  1. Age 50, Value 100
  2. Age 40, Value 150
  3. Age 30, Value 175
Here's the weighted average age formula:
(100×50+150×40+175×30) / (100+150+175) = 38

I would this result to be a KPI on one of my dashboards. What's the best way to accomplish this?