Question 550113
Let {{{ a }}} = weight of 9  men
Let {{{ b }}} = weight of the man replacing the 10th man
given:
{{{ ( a + 80 ) / 10 - 3 = ( a + b ) / 10 }}}
Multiply both sides by {{{ 10 }}}
{{{ a + 80 - 30 = a + b }}}
Subtract {{{ a }}} from both sides
{{{ 50 = b }}}
The new man weighs 50 kg