Question 1053887
What?  The solution will be taken only part of the way.


The group of students originally was some p number of students.  If each student works at rate of r  JOBS/DAY, then for the 25 days,  {{{p*r*25=1}}}.


Your next sentence is imprecise, so assuming that some x FEWER students actually did the work and this took 35 days, then let us say this:
{{{(p-x)*r*35=1}}}.


You have three unknown variables but only two equations.  Depending on what you are really given and should have said, you can probably understand the analysis here and handle the exercise problem.  


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One might guess that "1Q" means  "one quarter of...", so this could make for one less unknown variable.