Which of the following interchanges of signs would make the given equation correct?
40 + 45 × 5 – 12 ÷ 4 = 1

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

Given:
40 + 45 × 5 – 12 ÷ 4 = 1

Let's check each options:
Option (a) ÷ and ×
40 + 45 ÷ 5 – 12 × 4 = 1
40+ 9 -12 × 4 = 1
40 + 9 – 48
49 - 48
1=1(This balances the equation.)
Option (b) − and ×
40 + 45 - 5 × 12 ÷ 4 = 1
40 + 45 – 5 × 3
40 + 45 – 15
85 -15
70$$\not=$$​1(This does not balance the equation)
Option (c) + and ×
40 × 45 + 5 – 12 ÷ 4 = 1
40 × 45 + 5 -3
1800+5-3
1805-3
1802$$\not=$$ 1 (This does not balance the equation) ​
Option (d) − and +
40 - 45 × 5 +12 ÷ 4 = 1
40-45× 5 + 3
40- 225 +3
43-225
-182 $$\not=$$ 1(This does not balance the equation)

Thus, the correct option is: (a)