Lookup the Closest Match
The following formula returns a value from A2:A10 that is closest to the target value in C2...
=INDEX(A2:A10,MATCH(MIN(ABS(A2:A10-C2)),ABS(A2:A10-C2),0))
Note that the formula needs to be confirmed with CONTROL+SHIFT+ENTER. If done correctly, Excel will automatically place curly braces {...} around the formula.
Based on the sample data, the formula returns 25.
Sample Workbook: Download