Percents

At a contest with 1,500 participants, 1/2 of the people are aged 8 to 12. Next year, the number of
people aged 8 to 12 will increase by 1/3. After this change, what percentage of the total 1,500 people will the 8 to 12 year olds represent?

A. 33%
B. 40%
C. 50%
D. 55%
E. 66.66%

Answer

Total Participants: 1500

This Year: Ages 8 to 12 - 750
Next Year: Ages 8 to 12 - 750 + 1/3 x 750 = 750 + 250 = 1000

Choice E: The new percentage is 1,000/1,500, or 2/3, which corresponds to 66 2/3%.

The topic of percentages is one of the easiest that you will tackle on the GMAT. We are all accustomed to calculating percentages in our daily lives, and any potential question on this topic would seem to be a cakewalk to most. While that is generally true, there are also some traps and pitfalls that the GMAT will lay down for you. Be careful not to get caught in them! Here are some handy tips, tricks, and trap warnings to help you negotiate your way around GMAT questions on this topic:

Error Type 1: Using the wrong base when calculating percentage change

The percentage increase in a quantity when it is increased by a certain amount is [(new value – old value)/old value] x 100. Similarly the percentage decrease is [(old value-new value)/old value] x 100. This point seems to be fairly obvious. However, an exam situation can play tricks on anyone and cause them to make silly mistakes in a hurry.

A common error involves taking the new value in the denominator. If the price of a product increases from 120 to 140, the percentage increase is (20/120)*100 = 16.67%, not (20/140)*100...