Sequence Pattern Seq Numbers Hard — Set 72

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{
    "title": "Hard Sequence Pattern #72",
    "sequenceType": "seq-numbers",
    "displaySequence": [
        1,
        "_",
        21,
        31,
        "_",
        51,
        61,
        "_",
        81,
        91
    ],
    "fullSequence": [
        1,
        11,
        21,
        31,
        41,
        51,
        61,
        71,
        81,
        91
    ],
    "blankPositions": [
        1,
        4,
        7
    ],
    "answers": [
        11,
        41,
        71
    ],
    "rule": "Add 10 each time (start at 1)",
    "question": "Find the 3 missing terms in the sequence: 1, _, 21, 31, _, 51, 61, _, 81, 91",
    "sequenceLength": 10,
    "hint": "Look at the difference between each consecutive pair.",
    "_archetype": null,
    "_generatorId": null
}