Which two numbers (not digits) should be interchanged to make the given equation correct?
21 × 8 – 18 + (64 ÷ 2) + 32 = 64

21 × 8 – 18 + (64 ÷ 2) + 32 = 64

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

Let's put the options:

A) 8 and 18
New Expression: 

21 × 18 – 8 + (64 ÷ 2) + 32 = 64

21 × 18 – 8 + 32 + 32 = 64

378 – 8 + 32 + 32 = 64

378 – 8 + 32 + 32 = 64

442 – 8 = 64 

434 = 64 (Incorrect)

B) 8 and 2

New Expression: 

21 × 2 – 18 + (64 ÷ 8) + 32 = 64

21 × 2 – 18 + 8 + 32 = 64

42 – 18 + 8 + 32 = 64

82 – 18 = 64 

64 = 64 (Correct)
Thus, correct option is (b).

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