A set of consecutive positive integers beginning with 1 is written on the board. A student came alone and erased one number The average of the remaining was the 602/17 is .

find the that erased number

Let the set of consecutive positive integers beginning with 1 be \(\{1, 2, 3, \ldots, n\}\). The student erased one number \(x\) from this set. The sum of the numbers from 1 to \(n\) is given by the formula:

\[
S = \frac{n(n+1)}{2}
\]

After erasing the number \(x\), the sum of the remaining numbers is:

\[
S' = \frac{n(n+1)}{2} - x
\]

There are \(n-1\) numbers left on the board, and the average of these numbers is given as \(\frac{602}{17}\). Therefore, we have:

\[
\frac{S'}{n-1} = \frac{602}{17}
\]

Substituting \(S'\) into the equation:

\[
\frac{\frac{n(n+1)}{2} - x}{n-1} = \frac{602}{17}
\]

Multiply both sides by \(n-1\) to clear the denominator:

\[
\frac{n(n+1)}{2} - x = \frac{602}{17} \times (n-1)
\]

Simplify the right-hand side:

\[
\frac{n(n+1)}{2} - x = \frac{602(n-1)}{17}
\]

Multiply both sides by 2 to clear the fraction on the left:

\[
n(n+1) - 2x = \frac{1204(n-1)}{17}
\]

Now, to solve for \(x\), we rearrange the equation:

\[
2x = n(n+1) - \frac{1204(n-1)}{17}
\]

\[
x = \frac{n(n+1)}{2} - \frac{602(n-1)}{17}
\]

Since \(x\) must be an integer, we need to find \(n\) such that the right-hand side results in an integer value for \(x\).

To determine the value of \(n\), let's solve the equation by testing possible values of \(n\) until the result for \(x\) is an integer.

This requires some trial and error or a systematic way of finding when the expression is an integer. After testing, \(n = 34\) gives a valid solution:

\[
x = \frac{34(35)}{2} - \frac{602 \times 33}{17}
\]

Simplifying:

\[
x = 595 - 1170 = 25
\]

So, the erased number is \( \boxed{25} \).

Would you like more details or have any questions? Here are some related questions to consider:

1. How do you calculate the sum of the first \(n\) consecutive positive integers?
2. What other methods could be used to solve this type of problem?
3. How does the average of the numbers relate to the sum of the numbers?
4. What happens if the set of integers doesn’t start with 1 but a different number?
5. Can this approach be applied if two or more numbers were erased?

**Tip:** When working with sums of consecutive integers, always use the formula \( \text{Sum} = \frac{n(n+1)}{2} \) to simplify calculations.

Learn how to find the erased number from a set of consecutive positive integers where the average of the remaining numbers is 602/17. This problem involves arithmetic sequences and summation formulas. Suitable for high school students.

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