Simplify the following text for a Grade 7 native English-speaking person.
Original: Although any given solution to such a problem can be verified quickly , there is no known efficient way to locate a solution in the first place ; indeed , the most notable characteristic of NP-complete problems is that no fast solution to them is known .
Simplified: A solution to such a problem can be verified quickly , but finding such a solution is very difficult . NP-complete problems can be characterised by the fact that no fast solution to them is known .