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Tham khảo tài liệu 'sat - mc grawhill part 86', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Math I I Math Formula Concept Ratios and Proportions 4 x Correct answer 8 .6 12 x Cross-multiply 4 x 12 x .6 Distribute 4 x 7.2 .6x Subtract .6x 4 .4x 7.2 Subtract 4 .4x 3.2 Divide by .4 x 8 Common mistake 4 This is the result if you forget to add the quantity x to the denominator as well as the numerator. I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I Formula Concept Percent change e.g. To increase a value by 20 multiply by 1.20 To decrease a value by 10 multiply by I 0.90 Correct answer 92 1999 100 100 1.25 125 2000 125 125 .8 100 2001 100 100 .8 80 2002 80 80 1.15 92 2003 92 Common mistake 100 This is result if I you simply add up the percent changes instead of calculating the changes as above 25 - 20 - 20 15 0. I Math Math Math 1 Math 1 Formula Concept The Triangle Inequality B - Al C B Al Correct answer Formula Concept Average formula Correct answer sum ---- average 2 19 B - A C B A 12 - 8 C 12 8 4 C 20 x x 2 2 x 8 ----------- --------- 6 20 Substitute for A and B Simplify Common mistake This is the common error that can be made if you mistakenly set 4 C 20. x x 2 2x 8 18 4x 10 18 4x 8 x 2 Multiply by 3 Combine like terms Subtract 10 Divide by 4 Common mistake This is the result if you mistakenly think that there are 5 numbers instead of 3. 5 3 Math Math 1 1 ------------------J------------------------------------ Math Math 1 1 Formula Concept Weighted Averages If two numbers being averaged have different weights you must remember to account for that when finding the average. Correct answer 85 10 82 6 90 820 540 oc 85 16 16 Common mistake 86 This is the result if you mistakenly take the simple average of the two scores 82 and 90 rather than taking their weighted average. I I 1 Formula Concept Integer arithmetic Correct answer 28 Remember that the sum of the numbers from -12 to 12 is 0 because the negative integers cancel the positives. 13 14 15 42 so n I must be 15. To find the number of integers in the set just subtract the first from the last
