The following equation is incorrect. Which two signs should be interchanged to correct it?
6×18+40÷30−10=20

Let's test the options one by one:
Option B: + and ÷
Interchanging + and ÷, the equation becomes:

6×18÷40+30−10=20
6×
40
18
​
+30−10=
20
54
​
+20

=20
Option C: − and +
Interchanging − and +, the equation becomes:

6×18−40÷30+10=20
108−
3
4
​
+10

=20
Option D: − and ×
Interchanging − and ×, the equation becomes:

6−18+40÷30×10=20
Applying BODMAS:

6−18+(
30
40
​
)×10=20
6−18+
3
40
​


=20
Option A: + and ×
Interchanging + and ×, the equation becomes:

6+18×40÷30−10=20
Applying BODMAS:

40÷30=
3
4
​

6+18×
3
4
​
−10=20
6+(6×4)−10=20
6+24−10=20
30−10=20
20=20
(LHS = RHS)

Thus, option A is correct.