Question 1093381
Let {{{ x }}} = his age on last birthday
{{{ (1/7)*x + (1/12)*x + (2/3)*x + 9 = x }}}
Miultiply both sides by {{{ 3*4*7 = 84 }}}
{{{ 12x + 7x + 56x + 756 = 84x }}}
{{{ 75x + 756 = 84x }}}
{{{ 9x = 756 }}}
{{{ x = 84 }}}
----------------
He was 84 on last birthday
----------------------------
check:
{{{ (1/7)*x + (1/12)*x + (2/3)*x + 9 = x }}}
{{{ (1/7)*84 + (1/12)*84 + (2/3)*84 + 9 = 84 }}}
{{{ 12 + 7 + 56 + 9 = 84 }}}
{{{ 84 = 84 }}}
OK