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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. Read the given statements and conclusions carefully. You have to take the given statements to be true even if they seem to be at variance from commonly known facts. You have to decide which conclusion/s logically follow/s from the given statements.

    Statements:

    All beaches are sand.

    Some deserts are sand.

    All mountains are rocky. 

    Conclusions:

    (I) At least some beaches are desert.

    (II) At least some sands are rocky.

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

    256 * 4 * 9 * 3 * 14 = 51

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

    86 * 54 * 34 * 68 * 2 * 33

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

    60 × 4 + 9 ÷ 3 - 8 = 34

  5. If '+' means 'division', '-' means 'multiplication', '÷' means 'addition' and '× ' means 'subtraction', then what is the value of the following expression?

    14 - 4 ÷ 133 + 7 × 17

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

    625 ÷ 25 + 7 × 318 - 112 = 381

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

    5 * 23 * 24 * 4 * 10 * 111

  8. Which of the following interchanges of signs would make the given equation correct?

    100 + 100 × 50 - 2 ÷ 3 = 51 

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

    24 × 9 + 6 ÷ 24 - 18 = 22   

  10. Select the correct combination of mathematical signs that can sequentially replace the * signs and balance the given equation.

    11 * 13 * 238 * 17 * 34 = 123 


Important Questions from Logical Puzzle

  1. If ‘A’ denotes ‘addition’, ‘B’ denotes ‘subtraction’, ‘C’ denotes ‘multiplication’ and ‘D’ denotes ‘division’, then what will be the value of the following expression?

    6 C (57 B 8) D 7 B 32 A 9

  2. If, 5 + 7 = 47, 3 + 8 = 35, 9 + 2 = 29 then 7 + 4 = ?

  3. Which two signs need to be interchanged to make the following equation correct?

    63 ÷ 21 – 7 + 28 × 3 = 144

  4. If ‘–’ stands for ‘÷’, ‘+’ stands for ‘×’, ‘÷’ stands for ‘–’ and ‘×’ stands for ‘+’, then 80 – 20 + 10 ÷ 8 × 10 is equal to:

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

    3 ÷ 2 - 4 × 5 + 5 = 1
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