Hello, the answer is 47. According to the question, there are 79 people who send mineral water and 86 people who send fruit. The question says that everyone should bring at least one kind, and then subtract the total number of students in the third grade *** 1 18, and you can get 47 people.

Solution: (79+86)- 1 18

= 165- 1 18

=47

This problem uses off-type calculation, that is, recursive equation calculation, which is an operation that writes out the calculation process completely, that is, off-vertical calculation. When calculating mixed operations, it is usually to work out an expression step by step (step by step, you can't write an equal sign on the original formula), and the process of each step should be written out. Generally speaking, the equal sign should go forward and not be aligned with the first line. That is, to leave the original calculation.