SAT Subject Test Mathematics Level 1

If x is the number of whole miles, and each whole mile contains 5 fifth-miles,
the total number of fifth-miles is 5x. But you don’t have to pay 20 cents for
every one of those 5x fifth-miles—you already paid for the first fifth-mile. The
number of fifth-miles after the first is 5 x − 1:

charge  =   200 +   20(5x   −   1)  =   200 +   100x    −   20  =   100x    +   180

The answer is (C).

PERCENT INCREASE AND DECREASE

Some word problems present classic situations for which there are standard
approaches, or even formulas. Example 5, for instance, requires that you
know how to find a percent increase.

PERCENT INCREASE AND DECREASE FORMULAS

Example 6

During  the eighteenth  century,    the population  of  country X   increased

by  1,000   percent.    During  the nineteenth  century,    the population

1.