Mathematical Operations Questions for SSC CHSL

What Is This Topic?

In these questions, the exam gives you a substitution rule. For example: A means +, B means -, C means x, D means /. Then it gives you an expression like 12 C 4 A 6 B 2 and asks for the value. Your only job is to swap the coded symbols back to real ones and solve using BODMAS order. Think of it like a secret code — decode first, calculate second.

• Symbols are always redefined in the question itself — never assume a symbol means the same across different questions.
• After substitution, follow BODMAS strictly: Brackets, Orders, Division, Multiplication, Addition, Subtraction.
• Two main question types: (1) Find the value of an expression, (2) Which of the four options makes the equation true (balancing type).
• Sometimes the question interchanges two operations — e.g., + and x are swapped — and asks you to re-solve.
• Speed trap: Most errors happen because aspirants substitute correctly but solve in wrong order.

Type 1: Symbol Substitution (Find the Value)

The question defines 4 symbols and their meanings. You replace every coded symbol in the expression with the real operator and then calculate. This is the most common type in SSC CHSL. The only skill needed is careful substitution and BODMAS. Do not try to calculate while substituting — finish all substitutions first, then calculate.

• Always write out the substituted expression on rough paper before solving.
• Watch for negative results — subtraction after a large division can give a negative number.
• If two options look very close in value, recheck your BODMAS order, especially around division and multiplication.
• Typical time needed: 30-40 seconds per question.

Type 2: Interchange of Two Operations

Here, only two operators are swapped — e.g., + and - are interchanged, or x and / are interchanged. The question gives you an expression built with original symbols and asks you to solve it after the swap. Same process: swap first, then BODMAS. The twist is that after swapping, the expression can behave very differently — what looked like addition is now subtraction.

• Read carefully which two symbols are swapped — do not swap all four.
• Rewrite the expression after swapping before doing any calculation.
• Common SSC CHSL pattern: + swapped with x. This changes everything because multiplication has higher BODMAS priority than addition.
• If answer does not match any option, you likely forgot BODMAS priority after swap.

Type 3: Balancing / Correct Equation Type

The question gives you 4 options, each a full equation like 5 @ 3 # 2 = 7. You are given what @, # etc. mean, and you must find which equation is correct. Or sometimes the symbols are not defined and you must find which option gives a true equation by trying each. This type takes slightly longer because you evaluate up to 4 expressions.

• Eliminate options smartly — check the easiest-looking option first.
• If the right side (answer) is large, you likely need multiplication somewhere — use that to narrow down.
• Do not spend more than 60 seconds on this type — guess and move if stuck.
• SSC CHSL occasionally gives this as the odd-one-out variant — three equations are wrong, one is right.

• Solving left to right without BODMAS after substitution — multiplication and division must come before addition and subtraction.
• Swapping the wrong symbols in Type 2 questions — re-read the swap instruction, do not assume + and - are always the ones swapped.
• Substituting partially — changing some symbols but missing one, especially when the expression is long.
• In balancing type, calculating left-hand side but forgetting to compare with right-hand side value.
• Confusing the coded symbol with the operation — e.g., seeing @ in the expression and using it as a math symbol instead of converting it first.

• Decode then Calculate — D then C. Always decode ALL symbols first, write the real expression, then calculate. Never do both at once.
• BODMAS = Big Old Dogs Must Always Sit — Brackets, Orders, Division, Multiplication, Addition, Subtraction. Chant this before solving.
• The Two-Step Rule: Step 1 = Replace. Step 2 = BODMAS. If you follow two steps every time, you will not make errors.
• Swap questions: Think of it like two friends exchanging seats. Only those two people move — everyone else stays put.

• SSC CHSL typically puts 2-3 questions from this topic in the Reasoning section. All are solvable in under 60 seconds if you are methodical.
• The most tested pattern in recent SSC CHSL papers is symbol substitution (Type 1) with 4 symbols defined and a single expression to evaluate.
• Balancing type (find the correct equation from 4 options) appears occasionally and is slightly harder — if time is short, use elimination to quickly rule out clearly wrong options.
• Avoid doing mental calculation for these questions during the exam. Write out the substituted expression on rough paper — the 5 seconds spent writing saves 20 seconds of re-checking.
• If a question gives you two operations that are interchanged AND also defines symbols, handle the interchange first, then apply symbol definitions — read the question in the order it gives instructions.