Maths · Rung 12 of 30

Sequences

In an arithmetic sequence you always add the same amount (3, 7, 11, 15…: +4). In a geometric one you always multiply by the same number (2, 6, 18, 54…: ×3). The nth term of an arithmetic sequence is the first plus (n − 1) times the difference.

Where this sits

This is where the ladder starts: nothing is needed before it.

Exercises from this rung

Generated by the app, from easiest to hardest

  1. 11, 20, ?, 38, 47

    • 28
    • 29
    • 30
    • 38

    Why The difference between terms is 9: 20 + 9 = 29.

    easier

  2. 4, 8, ?, 16, 20

    • 12
    • 11
    • 16
    • 13

    Why The difference between terms is 4: 8 + 4 = 12.

    in between

  3. 3, 9, 27, 81, …

    • 243
    • 135
    • 84
    • 324

    Why Each term is the previous one times 3: 81 × 3 = 243. It is a geometric sequence.

    harder