Which two numbers should be interchanged to make the given equation correct?
$$45+35\times 7-81÷9=321$$

Let's test the options one by one using the BODMAS rule:Option A: Interchange 45 and 35The equation becomes:
$$35+45\times 7-81÷9$$
$$=35+315-9$$
$$=350-9=341\ne 321$$
Option B: Interchange 45 and 7The equation becomes:
$$7+35\times 45-81÷9$$
$$=7+1575-9=1573\ne 321$$
Option C: Interchange 7 and 9The equation becomes:
$$45+35\times 9-81÷7$$
Since $81$ is not perfectly divisible by $7$, this will result in a fraction, so it cannot equal $321$.Option D: Interchange 45 and 81The equation becomes:
$$81+35\times 7-45÷9$$
Applying BODMAS:Division: $45÷9=5$ Multiplication: $35\times 7=245$ Now substitute back: $81+245-5$ Addition and Subtraction: $326-5=321$ This matches the right-hand side ($321$). Therefore, interchanging 45 and 81 makes the equation correct.