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Mathematical Operations Questions and Answers

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61.

If × stands for 'addition', ÷ stands for 'subtraction', + stands for 'multiplication' and-stands for 'division', then 20 × 8 ÷ 8 - 4 + 2 = ?

Answer: C

Correct answer: 24

Replacing each symbol by what it stands for gives \( 20 + 8 - 8 \div 4 \times 2 \). Division and multiplication first: \[ 20 + 8 - 4 = \mathbf{24} \]

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62.

In a group of buffaloes and ducks the number of legs are 24 more than twice the number of heads. What is the number of buffaloes in the group ? 

Answer: C

Let the number of buffaloes be x

 and number of ducks be y.

Now, number of heads = x+y

Number of legs = 4x+2y  .......(1) 

But given that legs = 2(x+y)+24 ......(2)

solving (1) & (2),we get

4x+2y=2x+2y+24 

--> x=12.

Therefore number of buffaloes =12

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63.

If 4 x 9 x 3 = 4 and 5 x 3 x 1 = 3, then
9 x 9 x 7 = ?

Answer: A

Correct answer: 5

In each case the three numbers are added and the square root taken: \( \sqrt{4+9+3} = \sqrt{16} = 4 \) and \( \sqrt{5+3+1} = \sqrt{9} = 3 \). So \[ \sqrt{9+9+7} = \sqrt{25} = \mathbf{5} \]

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64.

Find out the two signs to be interchanged for making following equation correct

5 + 3 x 8 - 12 / 4 =3

Answer: B

Correct answer: - and /

Exchanging − and ÷ turns the equation into \( 5 + 3 \times 8 \div 12 - 4 \). Working by the usual order, \[ 5 + \frac{24}{12} - 4 = 5 + 2 - 4 = \mathbf{3} \]

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65.

In the following question, correct the given equation by interchanging two numbers.
8 x 3 ÷ 4 + 9 - 5 = 16

Answer: C

Correct answer: 5 and 3

Exchanging the numbers 5 and 3 gives \( 8 \times 5 \div 4 + 9 - 3 \), which works out as \[ 10 + 9 - 3 = \mathbf{16} \]

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66.

If "÷" denotes "multiplied by", "+" denotes "subtracted from", "x" denotes "added to" and "-" denotes "divided by",then

12 - 6 + 28 x 3 ÷ 9 = ?

Answer: C

Correct answer: 1

Replacing the words by their symbols gives \( 12 \div 6 - 28 + 3 \times 9 \), and by the usual order \[ 2 - 28 + 27 = \mathbf{1} \]

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68.

If ‘-‘ stands for ‘÷’, ‘+’ stands for ‘×’, ‘÷’ stand for ‘-‘ and ‘×’ stands for ‘+’, which one of the following question is correct?

Answer: A

Correct answer: 30 – 6 + 5 × 4 ÷ 2 = 27.

Substituting in this option gives \[ 30 \div 6 \times 5 + 4 - 2. \] Taking the divide and multiply first: \( 30\div6 = 5 \), \( 5\times5 = 25 \). Then \( 25 + 4 - 2 = 27 \), which matches the stated value. The other three fail once their symbols are replaced.

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69.

If 3 # 4 % 8 = 6 and 9 % 4 # 3 = 12, then 12 % 6 # 24 = ?

Answer: B

Correct answer: 3

The symbols stand for division and multiplication: \( 3 \div 4 \times 8 = 6 \) and \( 9 \times 4 \div 3 = 12 \), so # is ÷ and % is ×. Then \[ 12 \times 6 \div 24 = \mathbf{3} \]

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70.

If ‘+’ stands for ‘×’, ‘-‘ for ‘÷’, ‘×’ for ‘-‘ and ‘÷’ for ‘+’, find the value of 12 + 90 - 5 × 9 ÷ 3.

Answer: C

Correct answer: 210

Substituting gives \[ 12 \times 90 \div 5 - 9 + 3. \] Multiplication and division first, left to right: \( 12\times90 = 1080 \), \( 1080\div5 = 216 \). Then \( 216 - 9 + 3 = 210 \). Stopping at 216, before the last two terms are applied, gives the second option offered.

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