An on-again, off-again move by the Obama administration to scrap the federal gas tax in favor of a pay-per-mile fee would boost the tab to Americans as high as 250 percent, raising their current tax of 18.4 cents a gallon to as high as 46 cents, according to a new government study. —New pay-per-mile scheme would boost taxes 250 percent | WashingtonExaminer.com
The math example doesn’t illustrate the point the writer is trying to make.
If you start with 18.4 cents a gallon, and “boost” the tax 0%, you still have 18.4 cents/gallon.
If you start with 18.4 cents a gallon, and “boost it” 100%, you have added 18.4 cents, and you have 36.8 cents/gallon.
If you start with 18.4 and “boost the tab” 150%, that is 18.4 cents plus another 27.6 cents, which gives you 46 cents, but that’s only a 150% boost, not the 250% boost mentioned in the lead.
If you start with 18.4 cents a gallon, and boost it 250%, that is 350%, or 64.4 cents.
This is less a math problem than a writing problem. To get to 250% of something, you start with 100% and add 150%. The snappy phrase “boost the tab to Americans as high as 250%” does not mean the same thing as “the new tax is up to 250% of the old tax.”