Missing Number in Sequences

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ISEE Lower Level: Mathematics Achievement › Missing Number in Sequences

Questions 1 - 3
1

Find the missing term: 4, 9, _, 19, 24.

12

13

14

15

Explanation

This question tests ISEE Lower Level Mathematics: finding the missing number in an arithmetic sequence. An arithmetic sequence is a list of numbers with a constant difference between consecutive numbers, and understanding this requires identifying the pattern and applying it to find missing terms. In this specific sequence, [4, 9, _, 19, 24], the difference is 5, meaning each number increases by 5. The correct answer, 14, fits the pattern because 9 + 5 = 14, and 14 + 5 = 19, maintaining the consistent increase throughout. A common distractor, such as 15, might seem correct if students look at the middle position without calculating the actual pattern. To teach this skill, have students find differences between all given consecutive pairs first, practice adding 5 mentally, and always double-check by ensuring the pattern works both forward and backward from the missing number.

2

What number completes the sequence: 30, 25, _, 15, 10?

18

20

22

24

Explanation

This question tests ISEE Lower Level Mathematics: finding the missing number in an arithmetic sequence. An arithmetic sequence is a list of numbers with a constant difference between consecutive numbers, and understanding this requires identifying the pattern and applying it to find missing terms. In this specific sequence, [30, 25, _, 15, 10], the difference is -5, meaning each number decreases by 5. The correct answer, 20, fits the pattern because 25 - 5 = 20, and 20 - 5 = 15, continuing the descending sequence correctly. A common distractor, such as 22, might seem correct if students miscalculate the difference or don't maintain consistency. To teach this skill, practice skip counting backwards by 5s, use visual aids like number lines to show the regular intervals, and remind students to verify their pattern works for all consecutive pairs in the sequence.

3

What number completes the sequence: 20, 16, _, 8, 4?

6

10

12

14

Explanation

This question tests ISEE Lower Level Mathematics: finding the missing number in an arithmetic sequence. An arithmetic sequence is a list of numbers with a constant difference between consecutive numbers, and understanding this requires identifying the pattern and applying it to find missing terms. In this specific sequence, [20, 16, _, 8, 4], the difference is -4, meaning each number decreases by 4. The correct answer, 12, fits the pattern because 16 - 4 = 12, and 12 - 4 = 8, maintaining the consistent decrease. A common distractor, such as 14, might seem correct if students mistakenly calculate the difference as -2 or make an arithmetic error. To teach this skill, help students recognize that sequences can decrease as well as increase, practice finding differences in descending sequences, and emphasize the importance of checking that the pattern works for all given terms in the sequence.