2. The sum of three numbers is 1281. From the first number, 329 was subtracted, and to the second number, 401 was added. What needs to be done with the third number so that the sum does not change? Will the solution to the problem change if the word "sum" is replaced with "difference"?
2. First method of solving. Find out by how much the sum has increased ( $401-329=72$ ). To keep the sum the same, it is necessary to subtract 72 from the third number.

Second method of solving. Let $a, b, c$ be the first, second, and third numbers. According to the condition, their sum is 1281

$$
a+b+c=1281
$$

From the first number, 329 is subtracted $(a-329)$, and to the second number, 401 is added $(b+401)$. Their sum is

$$
a-329+b+401=a+b+72
$$

To keep the sum of the three numbers $a, b, c$ unchanged and equal to 1281, the third number must be reduced by $72(c-72)$.

If the word "sum" in the condition is replaced with "difference," the first step is to find out by how much the difference between $a$ and $b$ will decrease $(329+401=770)$. To keep the difference between $a, b$, and $c$ unchanged, 770 must be subtracted from the last number.

Answer: the third number must be reduced by 72. The solution to the problem will change.