Question 1049465
Let {{{ s }}} = Lisa's speed in mi/hr
{{{ s + 15 }}} = Tommy's speed in mi/hr
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Think of this as one of them standing still
and the other one moving at the sum of their speeds
{{{ 225 = ( s + s + 15 )*3 }}}
{{{ ( 2s + 15 )*3 = 225 }}}
{{{ 6s + 45 = 225 }}}
{{{ 6s = 180 }}}
{{{ s = 30 }}}
and
{{{ s + 15 = 45 }}}
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Tommy's speed is 45 mi/hr
Lisa's speed is 30 mi/hr
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check:
{{{ d[1] = 30*3 }}}
{{{ d[1] = 90 }}} mi
and
{{{ d[2] = 45*3 }}}
{{{ d[2] = 135 }}} mi
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{{{ d[1] + d[2] = 90 + 135 }}}
{{{ d[1] + d[2] = 225 }}} mi
OK