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ACT · Math · Preparing for Higher Math: Statistics and Probability
Measures of center and spread is part of Preparing for Higher Math: Statistics and Probability in the ACT Math section. The questions below are written in the style of the real test, each with the answer and a worked explanation.
Question types you will see here include mean of a data set, median, mode, or range, find the value that gives a target mean, effect of adding, removing and or changing a value.
Common traps: dividing by the number of distinct values instead of the count; ignoring the frequency column; an addition error in a long list.
Question 1
Aisha's scores on the first 5 quizzes were 89, 72, 79, 97, 66. What score does Aisha need on the next quiz so that the mean of all 6 scores is exactly 75?
47
50
75
403/5
Answer: A. 47
The total needed is 75 × 6 = 450. The current total is 403. The needed score is 450 - 403 = 47.
Question 2
Jamal's scores on the first 6 quizzes were 84, 97, 96, 76, 76, 86. What score does Jamal need on the next quiz so that the mean of all 7 scores is exactly 83?
66
69
83
515/6
Answer: A. 66
The total needed is 83 × 7 = 581. The current total is 515. The needed score is 581 - 515 = 66.
A few questions show the style. The free scan shows which ACT skills cost you the most points, then builds a plan around them.