India's population has been catching up with China, with 1132 million in mid-2007 and growing at 1.6% per year, versus China then with 1318 million and growing at only 0.6%. If these rates continue, when will India have more people than China?

Answer 1

They will be the same when the number of years x (measured from mid-2007) satisfies the following equation:
1.132*(1.016)^x = 1.318*1.006)^x
1.1643 = (1.016/1.006)^x = 1.0099^x

Use logs to solve. I get 15.5 years, making it late 2022 or early 2023.