Question 736479
Average weight  = ( total of boy's weight ) / ( number of boys )
Let {{{ x }}} = the weight of the 4th boy in kilos
---------------
{{{ ( 55 + 45 + 51 + x ) / 4 = 52 }}}
{{{ ( 151 + x ) / 4 = 52 }}}
{{{ 151 + x = 208 }}}
{{{ x = 57 }}}
The 4th boy weighs 57 kilos