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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: The SAT always has direct proportion problems. |
| 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 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. Click here to return to Web Book Access |