Cracking The SAT Premium

B) 15%

C) 20%

D) 115%

Here’s How to Crack It

First, you need to get the data from the chart. In 2004, the chart shows that there were approximately
730,000 visitors to Arches. In 2006, the chart shows that there were about 830,000 visitors to the park.
Now, it’s time to use the percent change formula. The difference is about 100,000 and the original is the
730,000 visitors in 2004:

%   increase    =       ×   100 ≈   15%

The correct answer is (B).

Percentages: Advanced Principles

Another aspect of percent questions may relate to things that increase or decrease by a certain percent
over time. This is known as “growth and decay.” Real world examples include population growth,
radioactive decay, and credit payments, to name a few. While Plugging In can help on these, it is also
useful to know the growth and decay formula.

When    the growth  or  decay   rate    is  a   percent of  the total   population:

final   amount  =   original    amount  (1  ±   rate)number of  changes

Let’s see how this formula can make quick work of an otherwise tedious question.

23.Becca    deposits    $100    into    a   bank    account that    earns   an  annual  interest    rate    of  4%. If  she

does    not make    any additional  deposits    and makes   no  withdrawals,    how long    will    it  take

her,    in  years,  to  increase    the value   of  her account by  at  least   60% ?

A) 12

B) 15

C) 25

D) 30

Here’s How to Crack It

You could add 4% to the account over and over again until you get to the desired amount, but that would
take a long time. Knowing the formula will make it a lot easier. First, set up the equation with the things