Which two numbers should be interchanged in the equation to make it correct: 25 - 28 + 21 x 10 / 5 = 43?

The equation becomes:

The equation becomes:

So, currently, the equation is $39 = 43$, which is incorrect. We need to find a swap that makes the LHS equal to 43.

Let's test each option:

• Option 1: Swap 5 and 28 The equation becomes:

  $$25 - 5 + 21 \times 10 \div 28$$ $$25 - 5 + 21 \times \frac{10}{28}$$ $$20 + 21 \times \frac{5}{14}$$ $$20 + \frac{3 \times 7 \times 5}{2 \times 7}$$ $$20 + \frac{15}{2} = 20 + 7.5 = 27.5$$

  Since $27.5 \neq 43$, this option is incorrect.

• Option 2: Swap 21 and 25 The equation becomes:

  $$21 - 28 + 25 \times 10 \div 5$$

$$
21 - 28 = -7
$$
$$
-7 + 50 = 43
$$
Since $43 = 43$, this option makes the equation correct.

• Option 3: Swap 10 and 43 The number 43 is the target value on the right-hand side of the equation, not a number within the expression to be swapped. Therefore, this option is not valid for this type of problem.

• Option 4: Swap 21 and 28 The equation becomes:

  $$25 - 21 + 28 \times 10 \div 5$$

$$
25 - 21 = 4
$$
$$
4 + 56 = 60
$$
Since $60 \neq 43$, this option is incorrect.

Based on the evaluation, swapping 21 and 25 makes the equation correct.

The final answer is $\text{21 এবং 25}$