Question 214344
Let {{{x}}} = the number of problems he solved correctly
{{{30 - x}}} will = the number he solved incorrectly
given:
{{{50x = 25*(30 - x)}}}
{{{50x = 750 - 25x}}}
{{{75x = 750}}}
{{{x = 10}}}
{{{30 - x = 20}}}
The boy solved 10 correctly
check:
{{{50x = 25*(30 - x)}}}
{{{50*10 = 25*(30 - 10)}}}
{{{500 = 25*20}}}
{{{500 = 500}}}
OK