Question 674496
Let {{{ b }}} = Bob's age now
{{{ b + 10 }}} = Joe's age now
{{{ b + 10 }}} = Bob's age in 10 years
{{{ b + 10 + 10 }}} = Joe's age in 10 years
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{{{ b + 10 = (3/4)*( b + 20 ) }}}
{{{ 4*( b + 10 ) = 3*( b + 20 ) }}}
{{{ 4b + 40 = 3b + 60 }}}
{{{ b = 20 }}}
{{{ b  + 10 = 30 }}}
Bob is 20 and Joe is 30
check:
In 10 years Bob will be 30
In 10 years Joe will be 40
Bob will be 3/4 of 40 which is 30
OK