**Quote:**

**Why can't I take 30 × 15 = 450; 450 × 75% = 337.5 and subtract 450 – 337.5**?

**30 × 15 = 450** miles the car could travel on its full tank before the modification.

**450 × 0.75 = 337.5** miles

**is some irrelevant value**. If we want to calculate how far the car can travel on its full tank after the modification we have to divide by 0.75, not to multiply. (Remember, that the car is able to travel MORE after the modification, NOT less.)

So 450 / 0.75 = 600 miles the car can travel on its full tank after the modification.

The increase is 600 – 450 = 150 miles. The correct answer is B.

**NOTE, that the key for solving this question is to calculate new consumption rate.**The consumption rate before the modification was 30 miles per gallon = 30 miles / 1 gallon.

**Quote:**

If it is modified to use a solar panel, it will use only 75 percent as much fuel as it does now.

Therefore the car will travel each 30 miles using just 0.75 of a gallon, not 1 gallon. The consumption rate after the modification is 30 miles / 0.75 gallon = 30/0.75 miles per gallon = 40 miles per gallon.