Question 995668
The description leaves three unknown variables.


EXPECTED:
p students to do 1 job in 25 days.
Let r be the rate for 1 student.
{{{pr*25=1}}}, the work rate equation for p students.


FEWER STUDENTS:
Now, p-Q students came to do the job and time required was 35 days.
{{{(p-Q)r*35=1}}}.


The system of these two equations can be solved for p.  See the THREE unknown variables, p, r, and Q.  You might assume that either r or Q would be a constant.


{{{pr*25=(p-Q)r*35}}}
{{{25rp=pr*35-Qr*35}}}
{{{25rp-35rp=-35Qr}}}
Multiply by {{{-5}}};
{{{7rp-5rp=7Qr}}}
{{{p(7r-5r)=7Qr}}}
{{{p=(7Qr)/(2r)}}}
{{{highlight(p=7Q/2)}}},  original number of students expected.