AccelePrep for the ACT Test 2nd Edition Student Text

C HAPTER 5 | H YPER P REP M ATH • 97

PERCENTAGES

Many percent problems fall into one of two categories: • This is what percent of that? • What was the percent change? ‡”‡ ‹• ƒ ‡šƒ’Ž‡ ˆ”‘ –Š‡ ϐ‹”•–…ƒ–‡‰‘”›Ǥ 3. A shirt that normally sells for $25 is on sale for $5 off. The sale price is what percent of the normal selling price? A. 5% B. 20% C. 25% D. 30% E. 80% Of course, a problem might be dressed up with a lot of words to make it •‡‡ †‹ˆϐ‹…—Ž–ǡ „—– ‹ˆ ›‘—…ƒ Ž‘…ƒ–‡ –Š‡ ‡› ™‘”†•ǡ ‹– „‡…‘‡• ‡ƒ•›Ǥ 4. Oxygen is carried in human blood by attaching to hemoglobin molecules. Oxygen saturation is a measure of how much oxygen the blood is carrying as a percentage of the maximum it could carry. One hemoglobin molecule can carry a maximum of four molecules of oxygen. Thus, a hemoglobin molecule carrying three molecules of oxygen is carrying 4 3 or 75% of the maximum amount of oxygen it could carry. If a test shows that 100 hemoglobin molecules are carrying 380 oxygen molecules, what is the oxygen saturation of the blood? F. 2.6% G. 38% H. 95% Ǥ ͻ͹ǤͶΨ K. 105% The other type of percent question asks about percent change.

Example:

Example: STRATEGY ALERT Easy does it. Problems near the beginning of the math •‡…–‹‘ ƒ”‡ –Š‡ ‡ƒ•› ‘‡•Ǥ —•– do the arithmetic.

CLOSER LOOK Use key words to set up an is/of equation to represent the percentage.

STRATEGY ALERT Use the CHOOT (CHange Over Old Total) formula to calculate percent change: 100 : Old Total Change STRATEGY ALERT Once you’ve determined that the population decreased, draw a line through the answers that say the population increased.

5. The 2000 census shows that the population of Muhlenberg County was 36,331. The 2010 census shows that the population of the county was 33,299. What was the approximate percentage change in the population from 2000 to 2010?

Example:

A. An increase of 8% B. An increase of 11% C. A decrease of 3% D. A decrease of 11% E. A decrease of 8%