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Question

What will come in the place of the question mark (?) in the following equation, if '+' and '−' are interchanged and '×' and '÷' are interchanged?
65 × 5 − 19 ÷ 3 + 25 = ?

This question was previously asked in
RRB NTPC 2024 CBT 1 Question Paper (28-Aug-2025) (Shift 3)
The correct answer is
45

Solving Equation with Operator Interchange

The problem requires solving the equation $65 \times 5 - 19 \div 3 + 25 = ?$ after interchanging specific arithmetic operators.

Operator Interchange Rule

The given rules for interchanging operators are:

  • '+' is interchanged with '−'
  • '−' is interchanged with '+'
  • '×' is interchanged with '÷'
  • '÷' is interchanged with '×'

Applying the Interchange

Applying these rules to the original equation:

Original Equation: $65 \times 5 - 19 \div 3 + 25 = ? $

After interchange: $65 \div 5 + 19 \times 3 - 25 = ? $

Solving the New Equation

Now, solve the new equation using the standard order of operations (BODMAS/PEMDAS: Brackets, Orders, Division/Multiplication, Addition/Subtraction).

  1. Division: Perform $65 \div 5$.

    $65 \div 5 = 13$

  2. Multiplication: Perform $19 \times 3$.

    $19 \times 3 = 57$

  3. The equation now becomes: $13 + 57 - 25$.
  4. Addition: Perform $13 + 57$.

    $13 + 57 = 70$

  5. Subtraction: Perform $70 - 25$.

    $70 - 25 = 45$

Thus, the value that comes in place of the question mark is 45.

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    32 ÷ 2 × 72 − 9 + 5 = ?
  2. If '+' means '$\div$', '$-$' means '$\times$', '$\div$' means '+' and '$\times$' means '$-$', then find the value of $2 - 1 \times 4 \div 4 + 2$?
  3. Study the given pattern carefully and select the numbers from among the options that can replace the question marks (?).

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Important Questions from Mathematical Operations

  1. Select the set, from the given options, in which the numbers are related in the same way as are the numbers of the following sets.

    (NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding/subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

    (6, 13, 78)

    (5, 22, 110)

  2. If + means -, - means ×, × means ÷, ÷ means +, then what will come in place of the question mark (?) in the following equation?

    28 - 6 ÷ 4 + 14 × 14 = ?

  3. In the following number-pairs, the second number is obtained by applying certain mathematical operations to the first number. Which numbers should replace X and Y so that the pattern followed by the two numbers on the left side of :: is the same as that on the right side of :: ?

    (NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 Operations on 13 such as adding/subtracting /multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

    X : 649 :: 956 : Y

  4. Which two numbers should be interchanged to make the given equation correct?

    75 ÷ 5 + 15 × 4 - 17 × 3 + (60 ÷ 6) × 10 = 100

    (Note: Interchange should be done of the entire number and not individual digits of a given number.)

  5. If '+' means minus, '-' means multiplication, '÷' means plus, and 'x' means division, then solve the equation: 
    15 - 3 + 10 x 5 ÷ 5

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