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|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: The SAT always
has direct proportion problems.
|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
Answer: The tree is 96 feet tall.
Practice with these examples:
An easy problem for scores from 200 to 400
A moderate problem for scores from 400 to 600
A difficult problem for scores from 600 to 800
For more practice:
Click here for problems in The Official SAT Study Guide.
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