Let’s figure out how long it will take for the average Indian to be as wealthy as the average Western European is today. All numbers are adjusting for inflation, so we’re measuring output in “piles of stuff,” not “piles of money.” India’s GDP per capita is $3,500, and (somewhat optimistically) let’s say that real output per person there grows at 5% per year. Using the rule of 70, how many years will it take for India to reach Italy’s current level of GDP per capita, about $28,000 per year?