Missing Number Series and Speed Strategy

A missing-number series prints a blank in place of one term and asks you to fill it. It is the friendliest series format because you can use terms on both sides of the gap to pin down the rule. This closing topic also brings together a quick decision strategy so you spend your series time where it actually earns marks.

Use Both Neighbours of the Gap

Unlike a wrong-number question, here you know every term except one, so read the terms before the blank and the terms after it. The rule that connects the visible terms on both sides has to produce the missing value, which often lets you confirm your pattern twice — once from the left and once from the right — before you commit.

A 30-Second Decision Strategy

Give yourself a fixed sequence of checks and a firm exit. Scan the differences; if constant, answer. If not, check the ratio; if clean, answer. If neither, test squares, cubes and a two-step rule for about ten seconds. If nothing resolves by then, mark it for review and move on — one stubborn series is never worth the three easy marks you could bank elsewhere in the same time.

Scan differences → ratio → powers → two-step; if unresolved in ~25s, skip and return

Which Series to Skip

Skip a series when the numbers are large and irregular and no pattern surfaces in your first two checks. In a sectional-timed exam, the discipline to leave one hard series is worth more than the mark itself, because it protects the flow of the whole section. Return to skipped questions only after you have cleared the guaranteed marks.

Solved Examples

Example 1: 7, 14, 28, ?, 112. Rule ×2, so the blank is 28 × 2 = 56, confirmed by 56 × 2 = 112.

Example 2: 5, 6, 11, 28, ?, 154. Rule ×n then adds; checking, terms fit ×2+? but confirm with neighbours to place the missing value near 57 region — always verify from both sides.

Example 3: 3, 6, 12, 24, ?, 96. Rule ×2 gives the blank 24 × 2 = 48.

✗ Solving a hard series for 90 seconds  |  ✓ Skipping after 25 seconds to bank three easy marks

Building Series Speed Before the Exam

The 25-second target is only realistic if the underlying arithmetic is automatic, so your practice should focus as much on recall as on patterns. Drill squares to 30, cubes to 15 and the first fifteen primes until they arrive instantly, because a series question is really a pattern layered on top of these facts. Then practise mixed sets under a timer, forcing yourself to abandon any question at 25 seconds so the skip instinct becomes a habit rather than a decision. Candidates who train the timer, not just the topic, walk into the exam already used to the pace the sectional clock demands.