Question 1092560
Their speeds will add since they
are going in opposite directions
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You can think of this as Susan standing 
still and Bob traveling at the sum of their speeds
Let {{{ t }}} = time in hrs for them to meet
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{{{ 400 = ( 60 + 40 )*t }}}
{{{ 100t = 400 }}}
{{{ t = 4 }}} hrs
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In 4 hrs, Bob travels 
{{{ d[1] = 60*4 }}}
{{{ d[1] = 240 }}}
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In 4 hrs, Susan travels
{{{ d[2] = 40*4 }}}
{{{ d[2] = 160 }}}
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check:
{{{ d[1] + d[2] = 240 + 160 }}}
{{{ d[1] + d[2] = 400 }}} mi
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They will meet 240 mi from Chicago
and 160 mi from Pittsburgh