The following equation is incorrect. Which two signs should be interchanged to correct the equation?

1 / 14 * 30 + 20 - 10 = 12

Correct option is D

Given:

1 / 14 * 30 + 20 - 10 = 12

Logic:

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

Lets check by options:

Option (a): '/' , '*'

After change mathematical operation:

1 * 14 / 30 + 20 - 10 = 12

1*0.466 + 20 - 10 = 12

0.466 + 20 - 10 = 12

20.466 - 10 = 12

10.466 $$\neq$$​ 12

(False)

Option (b): '*' , '-'

After change mathematical operation:

1 / 14 - 30 + 20 * 10 = 12

1 / 14 - 30 + 20 * 10 = 12

0.071 - 30 + 20 * 10 = 12

0.071- 30 + 200 = 12

- 30 + 200.071 = 12

170.071 $$\neq$$​ 12

​(False)​

Option (c): '-' , '+'

After change mathematical operation:

0.071 * 30 - 20 + 10 = 12

2.13 - 20 + 10 = 12

12.13- 20 = 12

-7.877 $$\neq$$ 12

​(False)​

Option (d): '+' , '/'

After change mathematical operation:

1 + 14 * 30 / 20 - 10 = 12

1 + 14 * 1.5 - 10 = 12

1 + 21 - 10 = 12

22 - 10 = 12

12 = 12

(True)

Thus, the correct answer is (d).