CogAT number series

Worked example

The same question, one step at a time.

1. 1Write the gap between each pair down first: 14 to 32 is +18, 32 to 20 is −12, 20 to 36 is +16, 36 to 26 is −10. They swing up and down, which is the sign that one pattern is not enough to explain the list.
2. 2Read every OTHER number instead. The 1st, 3rd and 5th are 14, 20, 26 — going up by 6 each time.
3. 3The 2nd and 4th are 32, 36 — going up by 4. Two series are woven together here.
4. 4The number asked for is the 6th, so it belongs to the second series, following 36.
5. 5Final answer: 36 + 4 = 40.

Common traps

Every wrong choice is built from a mistake children really make.

• Assuming the same jump

  Adding the last gap again works only when the gaps never change. Write every gap down first.

  In the example: choice B (16).

• The wrong kind of step

  Doubling where the series adds, or adding where it multiplies, gives a choice that looks reasonable.

  In the example: choice C (52).

• Nearly right

  A number one away from the answer is a slip in the last step. Check it against the rule once more.

  In the example: choices A (41) and E (39).