First, let’s look at the total increase - it’s either 100% (you added 150,000 to 150,000) or 50% (half of the 300,000 came in the last decade). Most often increases are described by the percentage of the starting amount, but the other convention can sometimes be used as well. For small percentages around 5% or lower, the two values will be almost the same, but in this case it makes a big different.
