Question 1072018
{{{N}}}= number of questions in the whole test
{{{x}}}= number of questions the student did not attempt
{{{N-x}}}= number of questions the student answered.
If he had answered {{{28}}} wrong and {{{N-28}}} right,
his score would have been
{{{(N-28)-0.25*28=60}}}
You can solve that for {{{N}}} many ways.
For example
{{{N-1.25*28=60}}}
{{{N-35=60}}}
{{{N=60+35}}}
{{{N=95}}}
The student knows that if {{{20}}} of his answers were wrong,
his scores would be
{{{N-x-20-0.25*20=60}}}
{{{95-x-20-5=60}}}
{{{70-x=60}}}
{{{70-60=x}}}
{{{x=10}}}
So the strident left out the answer for 10 questions.
He only answered the other {{{95-10=85}}} questions.