|The text is created by College Admissions Services. Copyright 2006. All rights reserved.
SAT is a registered trademark of the College Entrance Examination Board,
which is not affiliated with the production of these materials nor does it endorse them.
|Arithmetic: Direct Proportions
|While most people think the SAT is a test of advanced math, about one-fourth
of the questions are arithmetic. Most students need to review this arithmetic.
|SAT TIP: Every SAT has proportion
problems. Be sure to review direct
proportions to earn these "sure points".
|Questions? Write the SATtutor@SATpreparation.net|
|In direct proportions,
as one quantity increases, the other increases
(or as one quantity decreases the other decreases).
For example: A vertical pole 6 feet high casts a shadow four
feet long. At the same time, a tree casts a shadow 64 feet long.
What is the height, in feet, of the tree?
To solve a direct proportion, form an equation
with a ratio on one side and a ratio on the other side:
---------- = ----------- It helps to make a diagram.
6 ft. X ft.
-------- = --------- Write the units to be sure of the directionality.
4 ft. 64 ft.
Then cross multiply: 6 x 64 = 4 x X or 384 = 4X or X = 96
Answer: The tree is 96 feet tall.
|Practice with official SAT questions:
Easy: page 533, #9 > Go to explanation
Moderate: page 423, #2 > Go to explanation
Difficult: page 472, #6 > Go to explanation
Order The Official SAT Study Guide
Order a user name and password for the SAT Web Book
Return to Web Book Contents