Mathematical Operations – Railway Reasoning (part – 1)

Total Questions: 50

1. What will come in place of the question mark (?) in the following equation, if ‘+’ is interchanged with ‘ ÷ ’ ,  and ‘-’ is interchanged with ‘×’ ? [Group - D 17/08/2022 (Morning)]

100 x 121 + 11 - 7 ÷ 24 - 8 × 33 × 99 ÷  17 = ?

Correct Answer: (b) 100
Solution:

100 × 121 + 11 - 7 ÷ 24 - 8 × 33 × 99 ÷ 17
After interchanging the sign as per given instructions in the question,
100 - 121 ÷ 11 × 7 + 24 × 8 - 33 - 99 + 17
= 100 - 77 + 192 - 33 - 99 + 17 = 100

2. Select the correct combination of mathematical signs that can sequentially replace * to balance the following equation. [Group - D 17/08/2022 (Afternoon)]

20 * 4 *6 *2 *14 * 18

Correct Answer: (d) ÷, ×, +, =, +
Solution:

Given that 20 * 4 *6 *2 *14 * 18
After replacing the signs, we get:
20 ÷ 4 × 6 + 2 = 14 + 18
32 = 32 (L.H.S = R.H.S)

3. Which two numbers should be interchanged to make the following equation correct ? [Group - D 05/09/2022 (Evening)]

8 + 4 - (7 × 5 - 6) ÷ 3 = 3.75

Correct Answer: (c) 3 and 4
Solution:

Given equation
8 + 4 - (7 × 5 - 6) ÷ 3 = 3.75
By putting the options one by one, we found that only option (c) satisfies the given equation.
On interchanging the numbers 3 and 4,
we get,8 + 3 - (7 × 5 - 6) ÷ 4 = 3.75
8 + 3 - 29 ÷ 4 = 11 - 7.25 = 3.75

4. Which two numbers should be interchanged to make the following equation correct ? [Group - D 17/09/2022 ( Afternoon )]

9 + 7 - (6 ÷ 3 - 4) × 8 = 31

Correct Answer: (d) 8 and 7
Solution:

9 + 7 - (6 ÷ 3 - 4) × 8 = 31
By hit and trial method, go through option (d)
9 + 8 - (6 ÷ 3 - 4) × 7 = 31
⇒ 17 - (2 - 4) × 7 = 31
⇒ 17 + 14 = 31 ⇒ 31 = 31 (Satisfy)

5. If ‘+’ means ‘division’, ‘÷’ means ‘subtraction’, ‘–’ means ‘multiplication’ and ‘×’ means ‘addition’, then what is the value of X in the following equation? [NTPC CBT II Level 3 (14/06/2022) Shift 2]

200 + 10 – 25 × 60 ÷ 20 = X

Correct Answer: (b) 540
Solution:

200 + 10 – 25 × 60 ÷ 20 = X
As per question,
200 ÷ 10 × 25 + 60 - 20 = X
⇒ 20 × 25 + 40 = X ⇒ X = 540

6. If ‘’ means ‘+’, ‘&’ means ‘×’, and ‘@’ means ‘÷’, then what would be the value of the following expression? [NTPC CBT II Level 5 (15/06/2022) Shift 2]

119 < 56 @ 4 > 23 & 2

Correct Answer: (b) 151
Solution:

119 < 56 @ 4 > 23 & 2
Now, Interchange the signs according to the question.
⇒ 119 - 56 ÷ 4 + 23 × 2
⇒ 119 - 14 + 46 = 165 - 14 = 151

7. If ‘’ means ‘+’, and ‘$’ means ‘÷’, then what would be the value of the following expression? [NTPC CBT II Level 2 (16/06/2022) Shift 2]

37 > 165 $ 3 < 5

Correct Answer: (a) 87
Solution:

37 > 165 $ 3 < 5
On substituting all the symbols as instructed in the question
37 + 165 ÷ 3 – 5 ⇒ 37 + 55 – 5
⇒ 92 – 5 = 87

8. If ‘p + q’ implies p – q, ‘p – q’ implies p × q, ‘p × q’ implies p ÷ q and ‘p ÷ q’ implies p + q, then find the value of 25 + 48 × 6 ÷ 12 – 2. [NTPC CBT - I 29/12/2020 (Morning)]

Correct Answer: (a) 41
Solution:

After putting the changed signs,
25 - 48 ÷ 6 + 12 × 2 = 49 - 8 = 41

9. If one substitutes @ with either “+” or “×” (multiplication), in the expression 1@2@3@4@5@6, what is the maximum value that can be derived assuming that the correct order of mathematical operations are followed. [ NTPC CBT - I 07/01/2021 (Evening)]

Correct Answer: (d) 721
Solution:

1 + 2 × 3 × 4 × 5 × 6 = 1 + 720 = 721

10. If aPb implies a + b, aSb implies a-b, aMb implies a×b and aDb implies a÷ b, find the value of 5P6S3M4D8 [ NTPC CBT - I 07/01/2021 (Evening)]

Correct Answer: (c) 9.5
Solution:

5 P 6 S 3 M 4 D 8
= 5 + 6 - 3 × 4 ÷ 8
= 5 + 6 - 3 × 0.5 = 11 - 1.5 = 9.5