If the sign + is interchanged with – and the number 9 is interchanged with 6, then which of the following four equations would be correct?

Interchange '+' with '–'
Interchange '9' with '6'

Logic: BODMAS

​$$\begin{array}{|c|c|} \hline\textbf{Operation preference wise} & \textbf{Symbol} \\\hline\text{Brackets} &[],{}, () \\ \hline \text{Orders, of} & (power), √ (root) , of \\ \hline \text{Division}& ÷ \\ \hline \text{Multiplication} & × \\ \hline \text{Addition} & + \\ \hline \text{Subtraction} & - \\\hline\end{array}$$​​

Let's analyze all the options:

Option (a) 4 – 9 + 5 = 1 (Incorrect)
After interchangements, we get: 4 + 6 – 5 = 1

4 + 6 – 5 = 1

10 - 5 =1

5 $$\ne$$ 1​
Option (b) 6 – 9 + 4 = 1 (Incorrect)​
After interchangements, we get: 4 + 6 – 4 = 1

4 + 6 – 4 = 1

10 - 4 = 1

6 $$\ne$$ 1
Option (c) 6 – 9 + 7 = 1 (Incorrect)​
After interchangements, we get: 9 + 6 – 7 = 1

9 + 6 – 7 = 1

15 - 7 = 1

8 $$\ne$$ 1
Option (d) 9 + 6 – 4 = 1 (Correct)​

After interchangements, we get: 6 – 9 + 4 = 1

6 – 9 + 4 = 1

10 - 9 = 1

Thus, the correct option is (d) 9 + 6 – 4 = 1