Question 218764
This is a ratio problem
Let {{{t}}} = time in minutes spent studying after class
Let {{{s}}} = score in exam
It's a direct variation, so
{{{s = k*t}}}
Where {{{k}}} is a constant
given:
{{{72 = k*90}}}
{{{k = .8}}}
---------------
{{{s = k*100}}}
{{{s = .8*100}}}
{{{s = 80}}}
His score will be 80 with 100 minutes of study