SSC CGL (Prelims) General: Mathematical Operations questions with solutions

Q1. If ‘+’ means ‘×’, ‘×’ means ‘−’, ‘−’ means ‘÷’, and ‘÷’ means ‘+’, then \(16 + 4 × 18 − 2 ÷ 2 = ?\)

1. 55
2. 57
3. 59
4. 60

Answer: 57

After substitution, the expression becomes \(16 × 4 − 18 ÷ 2 + 2\). Now evaluate: \(16 × 4 = 64\), \(18 ÷ 2 = 9\), so \(64 − 9 + 2 = 57\).

Q2. After interchanging ‘+’ and ‘×’, which equation is true?

1. 4 + 6 × 2 = 20
2. 8 × 4 + 5 = 28
3. 5 + 4 × 6 = 54
4. 7 × 2 + 3 = 20

Answer: 8 × 4 + 5 = 28

After interchanging \(+\) and \(×\), the option \(8 × 4 + 5 = 28\) becomes \(8 + 4 × 5 = 28\), which is true because \(4 × 5 = 20\) and \(8 + 20 = 28\). The other options do not satisfy the condition after substitution.

Q3. If ‘×’ means ‘−’, ‘−’ means ‘+’, ‘+’ means ‘÷’, and ‘÷’ means ‘×’, which of the following is correct?

1. 12 × 4 - 2 = 10
2. 15 - 3 + 6 = 18
3. 10 + 5 ÷ 3 = 4
4. 8 ÷ 4 × 2 = 6

Answer: 12 × 4 - 2 = 10

Substituting the symbols gives 12 − 4 + 2, which equals 10. The other options do not remain true after applying the given symbol meanings.

Q4. Select the correct sequence of mathematical signs to replace A and B: $18\ A\ 6\ B\ 3 = 20$

1. ÷, +
2. ×, -
3. -, ×
4. + , ÷

Answer: + , ÷

Using addition first gives $18 + 6 = 24$, and then division by 3 gives $24 \div 3 = 8$, so that does not work. The correct pair is the one that makes the expression equal to 20; among the given options, $18 + 6 \div 3 = 20$ is valid because division is done first: $6 \div 3 = 2$, then $18 + 2 = 20$.

Q5. Which two signs should be swapped to make the equation correct? 24 + 8 ÷ 4 − 2 × 3 = 28

1. ÷ and +
2. + and ×
3. ÷ and ×
4. + and -

Answer: + and -

Swapping '+' and '−' changes the expression to 24 − 8 ÷ 4 + 2 × 3. Using BODMAS, this becomes 24 − 2 + 6 = 28, which is correct.