Question 889277
Just follow the process as described!

Let u = the starting number.

20% increase is {{{1.2u}}}.
20% decrease is {{{1.2u-0.20(1.20u)}}}.


The student now has {{{abs(1.2u-(1.2u-0.2u))=8}}}.
{{{abs(1.2u-1.2u+0.2u)=8}}}
{{{abs(0.2u)=8}}}
{{{0.2u=8}}}
{{{u=8/0.2}}}
{{{highlight(u=40)}}}