Missing Number Questions for SSC CHSL

Core Pattern Types

Missing Number questions test your ability to identify the rule governing a sequence. The five main pattern types cover 95% of SSC CHSL questions. Arithmetic patterns add or subtract a constant. Geometric patterns multiply or divide by a constant. Alternating patterns switch between two operations. Digit-sum patterns focus on the sum of digits in each number. Square/cube patterns involve perfect powers. Always check the simplest pattern first — SSC examiners rarely use complex nested rules.

• Arithmetic: constant difference between consecutive terms (e.g., 2, 5, 8, 11 — add 3 each time)
• Geometric: constant ratio between consecutive terms (e.g., 2, 6, 18, 54 — multiply by 3)
• Alternating: two different operations alternate (e.g., +2, ×3, +2, ×3)
• Digit-sum: sum of digits follows a pattern (e.g., 12, 23, 34 — digit sums are 3, 5, 7)
• Square/Cube: numbers are perfect squares or cubes (e.g., 1, 4, 9, 16, 25)
• Fibonacci-type: each term is sum of previous two (e.g., 1, 1, 2, 3, 5, 8)

Difference-of-Difference Method

When the first difference (gap between consecutive terms) is not constant, calculate the second difference (gap between the first differences). If the second difference is constant, you have a quadratic pattern. This method works for polynomial sequences up to degree 2, which covers most SSC CHSL questions. Write out the series, then the first differences below, then second differences below that. The pattern usually becomes obvious in 2-3 rows.

• First difference: subtract each term from the next (e.g., 1, 4, 9, 16 gives differences 3, 5, 7)
• Second difference: subtract each first difference from the next (e.g., 3, 5, 7 gives differences 2, 2)
• If second difference is constant, the missing term can be found by reversing the process
• This method is faster than guessing — use it when simple arithmetic/geometric fails
• Works for sequences like 1, 4, 9, 16, 25 (squares) and 1, 8, 27, 64 (cubes)

Position-Based and Digit Patterns

Some SSC CHSL questions hide the pattern in the position of the term or in the digits themselves. For example, the nth term might equal n squared, or the digit sum might follow a sequence. Always check: does the position number (1st, 2nd, 3rd) relate to the value? Are the digits themselves forming a pattern? These patterns are less common but appear 1-2 times per paper and catch unprepared candidates.

• Position-based: nth term = f(n). Example: 1st term = 1, 2nd term = 4, 3rd term = 9 means nth term = n squared
• Digit-sum pattern: sum of digits in each number follows a sequence (e.g., 11, 23, 35 have digit sums 2, 5, 8)
• Reverse digit pattern: number reads the same forwards and backwards (palindromes)
• Mixed operation: operations change based on position (e.g., odd positions add, even positions multiply)
• Always verify your pattern with at least 2-3 terms before committing to an answer

Three-Number Box Patterns

SSC CHSL often presents Missing Number in a box format with three numbers and one missing. The missing number is derived from the other three using a single operation or formula. Common formulas: sum of two outer numbers, product divided by third, or a ratio. These are faster to solve than series because there are fewer terms to check. The key is to try simple operations first: sum, difference, product, division, average.

• Sum rule: missing = sum of other two (e.g., 5, 7, ? where ? = 12)
• Product rule: missing = product of two divided by third (e.g., 6, 4, 12 where 12 = 6×4/2)
• Average rule: missing = average of other two (e.g., 10, 20, ? where ? = 15)
• Difference rule: missing = difference of two (e.g., 15, 8, ? where ? = 7)
• Always test the simplest operation first; SSC rarely uses complex multi-step formulas

• Assuming arithmetic pattern when it's geometric. Always check ratio before assuming constant difference. A series like 2, 4, 8, 16 is NOT +2 each time.
• Forgetting to check second difference. Many aspirants give up after first difference doesn't work, missing quadratic patterns that are common in SSC.
• Misreading negative numbers or zero. A series like 5, 3, 1, -1, -3 is arithmetic with d = -2, but candidates often miss the sign change.
• Not verifying the pattern across all given terms. You spot a pattern in the first 3 terms, but it breaks at term 4 — this means you chose wrong. Always verify before answering.
• Overthinking box problems. If sum, product, and average don't work in 20 seconds, move on. SSC box patterns are intentionally simple.

• SAD rule: Series, Arithmetic, Difference. When you see a series, first check if it's Arithmetic (constant difference). If not, use Difference-of-Difference method.
• GAPPS: Geometric, Arithmetic, Position, Polynomial, Special (Fibonacci, squares, cubes). Run through these in order when pattern is unclear.
• First, Second, Third: Always write out First differences. If not constant, write Second differences. If still not constant, check if it's position-based or special.
• Box = Simple: In box problems, try Sum, Product, Average, Difference in that order. 80% of SSC box questions use one of these four.

• SSC CHSL typically asks 2-3 Missing Number questions in the Reasoning section. They are usually easier than Analogy or Classification, so solve these first to build confidence.
• Time allocation: Spend max 45-60 seconds per Missing Number question. If pattern doesn't emerge in 40 seconds, mark and move — guessing wastes time.
• Recent papers show a mix of series (60%) and box (40%) formats. Series tend to be arithmetic or geometric; boxes tend to use sum/product rules.
• Negative numbers and zero appear frequently in recent papers. Don't assume all numbers are positive. A series like 10, 5, 0, -5, -10 is arithmetic with d = -5.
• Digit-sum and position-based patterns are rising in frequency. If standard patterns fail, check if the position number or digit sum is involved. This catches 1-2 extra marks per paper.