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Question

By interchanging the given two signs and numbers which of the following equation will be not correct?
× and ÷, 2 and 6
I. 7 – 4 × 3 ÷ 6 + 2 = 8
II. 6 – 8 × 2 + 9 ÷ 3 = 5

This question was previously asked in
SSC CGL 2022 Tier-II (Paper 2 JSO) Previous Year Paper (04-Mar-2023)
The correct answer is

Both I and II

Solving Equations by Interchanging Signs and Numbers

This problem requires us to evaluate two equations after applying specific rules for interchanging signs and numbers. We need to swap the multiplication sign (×) with the division sign (÷) and the number 2 with the number 6 in both equations. After performing the interchanges, we will check if the resulting equations are correct based on standard mathematical operations.

Rules for Interchange

  • × will be replaced by ÷
  • ÷ will be replaced by ×
  • The number 2 will be replaced by the number 6
  • The number 6 will be replaced by the number 2

Analysis of Equation I

The original Equation I is:

\(7 - 4 \times 3 \div 6 + 2 = 8\)

Now, let's apply the given interchanges to Equation I:

  • Replace × with ÷
  • Replace ÷ with ×
  • Replace 6 with 2
  • Replace 2 with 6

Applying these rules, the new equation becomes:

\(7 - 4 \div 3 \times 2 + 6\)

Let's evaluate this expression using the order of operations (BODMAS/PEMDAS):

  1. Perform division and multiplication from left to right:
  2. \(4 \div 3 = \frac{4}{3}\)
  3. Then, \(\frac{4}{3} \times 2 = \frac{8}{3}\)
  4. Perform addition and subtraction from left to right:
  5. \(7 - \frac{8}{3} + 6\)
  6. Combine terms: \(7 + 6 - \frac{8}{3} = 13 - \frac{8}{3}\)
  7. Find a common denominator (3): \(13 = \frac{13 \times 3}{3} = \frac{39}{3}\)
  8. Subtract: \(\frac{39}{3} - \frac{8}{3} = \frac{39 - 8}{3} = \frac{31}{3}\)

The calculated value of the left side is \(\frac{31}{3}\). The original equation stated the result is 8. Since \(\frac{31}{3} \neq 8\) (because \(8 = \frac{24}{3}\)), Equation I is NOT correct after the interchange.

Analysis of Equation II

The original Equation II is:

\(6 - 8 \times 2 + 9 \div 3 = 5\)

Now, let's apply the given interchanges to Equation II:

  • Replace × with ÷
  • Replace ÷ with ×
  • Replace 6 with 2
  • Replace 2 with 6

Applying these rules, the new equation becomes:

\(2 - 8 \div 6 + 9 \times 3\)

Let's evaluate this expression using the order of operations (BODMAS/PEMDAS):

  1. Perform division and multiplication from left to right:
  2. \(8 \div 6 = \frac{8}{6} = \frac{4}{3}\)
  3. \(9 \times 3 = 27\)
  4. Perform addition and subtraction from left to right:
  5. \(2 - \frac{4}{3} + 27\)
  6. Combine terms: \(2 + 27 - \frac{4}{3} = 29 - \frac{4}{3}\)
  7. Find a common denominator (3): \(29 = \frac{29 \times 3}{3} = \frac{87}{3}\)
  8. Subtract: \(\frac{87}{3} - \frac{4}{3} = \frac{87 - 4}{3} = \frac{83}{3}\)

The calculated value of the left side is \(\frac{83}{3}\). The original equation stated the result is 5. Since \(\frac{83}{3} \neq 5\) (because \(5 = \frac{15}{3}\)), Equation II is NOT correct after the interchange.

Conclusion

After interchanging the signs (× and ÷) and the numbers (2 and 6):

  • Equation I results in \(\frac{31}{3}\), which is not equal to 8. So, Equation I is not correct.
  • Equation II results in \(\frac{83}{3}\), which is not equal to 5. So, Equation II is not correct.

Therefore, both Equation I and Equation II will be not correct after the specified interchanges.

Equation Original After Interchange Calculated Value (Interchanged) Original Expected Value Correct/Not Correct (After Interchange)
I \(7 - 4 \times 3 \div 6 + 2 = 8\) \(7 - 4 \div 3 \times 2 + 6\) \(\frac{31}{3}\) 8 Not Correct
II \(6 - 8 \times 2 + 9 \div 3 = 5\) \(2 - 8 \div 6 + 9 \times 3\) \(\frac{83}{3}\) 5 Not Correct

Revision Table - Interchanging Operators and Numbers

Operation/Number Original Interchanged With
Sign 1 × ÷
Sign 2 ÷ ×
Number 1 2 6
Number 2 6 2

Additional Information - Order of Operations (BODMAS/PEMDAS)

When evaluating mathematical expressions, we follow a specific order of operations to ensure consistency in results. This order is often remembered using acronyms like BODMAS or PEMDAS.

  • BODMAS: Brackets, Orders (powers/roots), Division and Multiplication (from left to right), Addition and Subtraction (from left to right).
  • PEMDAS: Parentheses, Exponents (powers/roots), Multiplication and Division (from left to right), Addition and Subtraction (from left to right).

In this problem, we used Division and Multiplication before Addition and Subtraction, working from left to right for operations at the same level.

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Similar Questions

  1. Which of the following interchange of numbers and mathematical signs would make the given equation correct?

    30 ÷ 6 × 4 + 15 - 35 = 25

  2. Select the correct combination of mathematical signs that can sequentially replace the * signs and make the equation correct.

    48 * 12 * 8 * 15 * 3 * 44

  3. By Interchanging the given two numbers which of the following equation will be not correct?

    9 and 6

  4. By Interchanging the given two numbers which of the following equation will be correct?

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  5. Which two signs should be interchanged to make the given equation correct?

    95 * 5 + 19 ÷ 2 − 21 = 36

  6. By interchanging the given two signs and numbers which of the following equation will be not correct?

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  7. Select the correct combination of mathematical signs to sequentially replace the * signs and to balance the given equation.

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  8. Which two signs and two numbers should be interchanged in the following equation to make it correct?

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  9. By interchanging the given two signs which of the following equation will be not correct?

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  10. By interchanging the given two signs and numbers which of the following equation will be not correct?

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    I. 7 × 8 + 4 – 6 ÷ 3 = 57

    II. 4 × 8 – 9 ÷ 3 + 7 = 3


Important Questions from Logical Puzzle

  1. Seven persons P, Q, R, S, T, U and V like different watches namely W1, W2, W3, W4, W5, W6 and W7 (not necessarily in the same order). P and R do not like odd numbered watch. T likes W5. U does not like W2 or W3 or W6 or W7. P likes prime numbered watch. Q likes W4. S likes W2 or W7. Which of the following statement(s) is/are correct ?

    I. S likes W7.

    II. R likes W2.

    III. U likes W1.

    IV. V likes W3.

  2. If ‘+’ means ‘×’, ‘×’ means ‘÷’, ‘÷’ means ‘–’ and ‘–’ means ‘+’, then

    16 + 18 × 3 ÷ 6 = ?

  3. In a certain code language, ‘Today is last match’ is written as ‘Sa Te Mo Pt’, ‘Last king like your team’ is written as ‘De Ra Mo Lo Zs’, ‘Our team won today match’ is written as ‘Te Ra Pt Ae We’. What is the code for ‘Our won is Last’ in that code language?

  4. In a certain code language, ‘LETTER’ is written as ‘ZLZYIO’. What is the code for ‘ACTION’ in that code language?

  5. If A denotes ‘+’, B denotes ‘×’, C denotes ‘-’, and D denotes ‘÷’, then what will come in place of ‘?’ in the following equation?

    34 A 15 B 3 C 11 B 2 A (51 D 17) = ?

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