Correct Answer - Option 4 : 51 and 81
Given Equation: 51 - 4 × 7 + 81 ÷ 3 = 70
CONCEPT:
Follow the BODMAS rule to solve this question interchanging the respective numbers given in each option, as per the order given below,
Step - 1 - Parts of an equation enclosed in 'Brackets' must be solved first,
Step - 2 - Any mathematical 'Of' or 'Exponent' should be solved next,
Step - 3 - Then, the parts of the equation containing 'Division' and 'Multiplication' operations are solved,
Step - 4 - And lastly, the parts of the equation that contains 'Addition' and 'Subtraction' should be calculated.
So, on using BODMAS and solving each option,
1) 7 and 51,
After interchanging, the equation becomes,
7 - 4 × 51 + 81 ÷ 3 = 70
7 - 4 × 51 + 27 = 70
7 - 204 + 27 = 70
- 170 ≠ 70
2) 3 and 4
After interchanging, the equation becomes,
51 - 3 × 7 + 81 ÷ 4 = 70
51 - 3 × 7 + 20.25 = 70
51 - 21 + 20.25 = 70
50.25 ≠ 70
3) 51 and 3
After interchanging, the equation becomes,
3 - 4 × 7 + 81 ÷ 51 = 70
3 - 4 × 7 + 1.59 = 70
3 - 28 + 1.59 = 70
-23.41 ≠ 70
4) 51 and 81
After interchanging, the equation becomes,
81 - 4 × 7 + 51 ÷ 3 = 70
81 - 4 × 7 + 17 = 70
81 - 28 + 17 = 70
98 - 28 = 70
70 = 70
Hence, 51 and 81 should be interchanged to make the given equation correct.
