By Interchanging the given two numbers which of the following equation will be correct?

1 and 6 

I. 7 - 5 + 1 x 3 ÷ 6 = 20 

II. 1 x 7 + 6 - 4 ÷ 2 = 40  

Only I

In the first equation, 7 - 5 + 1 x 3 ÷ 6 = 20 

interchanging 1 and 6,

The equation becomes 7 - 5 + 6 x 3 ÷ 1 = 20

The equation is correct, i.e. LHS = RHS

BY interchanging in the second equation : 1 x 7 + 6 - 4 ÷ 2 = 40

The equation becomes 6 x 7 + 1 - 4 ÷ 2 = 40

Here, LHS = 41 and RHS = 40

Thus, interchanging does not make the equation correct.