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| Arithmetic: Direct Proportions |
| SATprepararion.net |
| 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. |
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| SAT TIP: Every SAT has proportion problems. Be sure to review direct proportions to earn these "sure points". |
| Questions? Write the SATtutor@SATpreparation.net |
| Math Review |
| 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: pole tree ---------- = ----------- It helps to make a diagram. shadow shadow 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 |