Question 771290
Let {{{ x }}} = the amount of money he had at first
Ian spent {{{ (3/5)*x }}} on a book
{{{ (2/5)*x }}} is left
He spent {{{ (1/4)*(2/5)*x = (1/10)*x }}} on a pen 
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{{{ (3/5)*x = ( 1/10 )*x + 350 }}}
{{{ (6/10)*x - (1/10)*x = 350 }}}
{{{ .5x = 350 }}}
{{{ x = 700 }}}
He had 700 pesos
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check:
The pen costs {{{ (1/10)*700 = 70 }}}
The book costs {{{ (3/5)*700 = 420 }}}
{{{ 70 + 420 = 490 }}}
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There is {{{ x *( 1 - ( 6/10 + 1/10 ) ) = (3/10)*x }}}
{{{ (3/10)*700 = 210 }}}
and
{{{ 490 + 210 = 700 }}}
OK