tailieunhanh - Sat - MC Grawhill part 36

(Sure, it's kind of nice to have a simple rule for when to guess on a multiple choice question, but isn't it better to be able actually to solve the problems?) Princeton, Up Your Score and REA just seem to be battling each other to be cute and clever with their delivery, but that's not what kids need. What students need is lots of practice coupled with smart feedback that recognizes their common mistakes. The flashcards-although there aren't enough of them-are very cool in pointing out the common errors that students make on SAT I math problems. . | 340 McGRAW-HILL S SAT Answer Key 2 Mean Median Mode Problems Concept Review 2 1. It should look like this 2. When two of the three values are given in a problem write them in the pyramid and perform the operation between them. The result is the other value in the pyramid. 3. A median is the middle number when the numbers are listed in order. If there are an even number of numbers in the set it is the average of the two middle numbers. 4. The number that appears the most frequently in a set. 5. When the numbers are evenly spaced the mean is always equal to the median. This is true more generally if the numbers are distributed symmetrically about the mean as in -10 -7 0 7 10 . 6. If the average of four numbers is 15 then their sum must be 4 15 60. If one of the numbers is 18 then the sum of the other three is 60 - 18 42. So the average of the other three is 42 3 14. SAT Practice 2 1. D The average of 2x 2x y and 3y is 2x 2x y 3y 4 4x 4y 4 x y. Substituting 2x 1 for y gives x 2x 1 3x 1. 2. C If the average of seven integers is 11 their sum is 7 11 77. If each of these integers is less than 20 then the greatest any can be is 19. The question doesn t say that the integers must be different so if x is the least possible of these integers x 19 19 19 19 19 19 77. Simplify x 114 77 Subtract 114 x -37 3. 4 The median is the average of the two middle numbers. A little trial and error shows that 1 4 6 and 8 have a median of 5 so k must be 4. 7. You need to read this problem super-carefully. If the average of the five numbers is 25 then their sum is 5 25 125. If none of the numbers is less than 10 and since they are all different integers the least that four of them can be is 10 11 12 and 13. Therefore if x is the largest possible number in the set Simplify Subtract 46 x 10 11 12 13 125 x 46 125 x 79 8. If the 20 students in Ms. Appel s class averaged 90 then they must have scored a total of 20 90 1 800 points. Similarly Mr. Bandera s class scored a total of 30 80 2 400. The .